Spider Identification, Biology and Control
Carolus Linnaeus published the 10th edition of Systema Naturae in which he classified plants and animals. Over the years biologists improved the systematic study of living organisms. The basis of this system is to place organisms into categories based on similarities in structures. In the case of animals the largest of these categories is the kingdom Animalia. This kingdom contains a number of subdivisions called phyla.
The phylum Arthropoda consists of animals with exoskeletons (hardened exteriors), segmented bodies and jointed appendages. This Phylum is divided into 5 major classes, namely the Arachnida (arachnids), Chilopoda (centipedes), Diplopoda (millipedes) Insecta (insects) and Crustacea (crustaceans).
The class Arachnida is further subdivided into 10 orders. The most important and common of these are the Araneae (spiders), Scorpionida (scorpions), Pseudoscorpionida (pseudoscorpions), Solpugida (sunspiders and windscorpions), Uropygi (whiptailed scorpions), Acari (tick and mites) and Phalangida (harvestmen)
Accordingly, the spiders are placed in phylum Arthropoda, class Arachnida and order Araneae. This order is further divided into 2 main sub-orders, namely the primitive spiders and the modern spiders. Every spider belongs to a family, which is further divided into genera, followed by species. For example the genus and species of a brown huntsman spider is Heteropoda jugulans (Figure 1). As a rule genus and species are printed in italics and the genus name is capitalized, while the species name is not.
Figure 1. The huntsman spider.
There are approximately 7,000 species of spiders. These arthropods are much more common than one might expect and, consequently, are quite important in controlling insect populations. For example, one study in Great Britain counted 130.8 spiders per square meter of meadowland. An average spider (if there is such a thing) consumes 0.09 grams of insects per day. After some calculations, one author concluded that in the Netherlands, with an area of 36,150 square kilometers and 15 million human habitants, there are 5,000 billion spiders. He further concluded that these spiders could consume all Dutchmen in 3 days. Luckily for us spiders do not eat humans! I am sure the same would be true of the US.
Spider silk is an extremely strong material that, on an equal weight basis, is stronger than steel. One scientist suggested that a pencil-thick strand of silk could stop a 747 in flight. It is used by spiders for many different activities, including the construction of egg sacs and webs, as a lifeline when jumping or dropping to escape, for wrapping their prey and transferring semen from the abdomen to the male’s palp and as a shelter in which a spider can retreat.
The silk is produced by the silk glands as a liquid that hardens when released from the spinnerets (silk spinning structure on the tip of the abdomen) (Figure 2).
Figure 2. Electron microscopic view of spinnerets.
Silk is elastic and only breaks when stretched 2 to 4 times its original length. Spiders frequently recycle silk which is very important for those that form large webs, such as the orb web spiders. In these cases, webs are easily destroyed and after a few days the droplets that bind them lose their adhesiveness. Old web is typically eaten and recycled for the building materials of new silk.
Dupont Corporation is studying spider webs. By using recombinant DNA technology, they managed to produce analogs of silk in yeast and bacteria and are planning to use this synthesized material for many kinds of construction purposes.
Spider Feeding and Venom
The jaws of a modern spider (Figure 3) are used to grab and crunch prey. Most spiders use poison to kill their victims. At the end of the jaws are two syringe-like structures that are hollow and quite sharp. These are used to puncture the body of a victim and inject the venom that is produced in special glands located in the cephalothorax. In many cases spiders do not inject the venom especially with a defensive bite. When this happens it is referred to as a dry bite. Whether a spider injects venom or not depends on the circumstances but primarily depends on how threatened the spider is and the species involved. Primitive spiders have forward-pointing jaws that move forward and backward. Therefore, they cannot chew but, as discussed below, feed on the liquid components of their prey.
Figure 3. The jaws or chelicerae of a spider.
Unlike humans who digest food mainly after it reaches the stomach, spiders have what is referred to as external digestion. Injected enzymes dissolve the prey. Then it is sucked empty, leaving nothing but a few bits and pieces. Between the mouth and stomach there is a filtering device that is made up of thousands of fine hairs. Only particles smaller than 1 mm can pass through this filter. This is so small that even the particles in India ink will be filtered out so that only liquids pass through. With these filters the spider prevents bacteria, viruses and other harmful life forms from entering its own body. The filter is regularly cleaned with the spider’s upper and lower liplike structures.
Because the food can be large in comparison to its own body volume, the spider’s abdomen can swell enormously. Excess digested proteins are stored making it possible for a spider to live for several weeks on a single prey. Waste materials are chemically converted to harmless crystals and are stored in special cells. In some orb web spiders, groups of these cells can be seen on the top of the abdomen and appear as white spots (Figure 4).
Figure 4. An orb-weaving spider illustrating the storage crystal (white) of waste products.
The black widow spider (Figure 5) is found in every state of the country with similar species throughout much of the world. There are 5 or 6 species of widow spiders belonging to the genus Lactrodectus in the United States, each being marked slightly different and all of which have a fairly toxic bite. There are 2 species that are restricted to southern Florida, namely the brown widow and the red widow. Lactrodectus mactans is the species most commonly associated with the name black widow. Its range is throughout the U.S. and overlaps with that of the northern widow in Gulf States and Canada.
Female black widow, Lactrodectus mactans.
Female black widow, Lactrodectus mactans. Image courtesy of CDC Healthwise Photo Library.
Only the female of the species is dangerous and is named after the practice of killing the male immediately after copulation. In actuality, the female is usually pretty well fed and, more times than not, the male escapes before being consumed. The males (Figure 6) are several times smaller than the female and brownish in color with pearly markings on the top of the abdomen. As with many spiders, the male’s pedipalps are club-shaped and used to transfer sperm to the female.
Figure 6. A size comparison of a female and male black widow. Image courtesy Peter Chew.
The immature females are often brown and striped with colored markings. All stages (except the youngest spiderlings) have a red marking on the underside of the abdomen. This red marking serves as a warning coloration to potential predators. Bright coloration in most animals serves the same function, advertising the fact that this animal is potentially dangerous and to stay away. The black widow female hangs upside down in her web thus making this marking clearly visible.
The female is nocturnal and lies in wait on the web for prey to pass. The male typically is not found in the web but hunts either for food or a female. The web is uniquely and characteristically irregular in shape, strong, and produces a crackling sound when probed. The female can produce from 1 to 10 marble shaped white egg sacs in the spring. These eggs hatch within 10 days or so, with the young spiderlings remaining inside the sac until after their first molt. The 200 or so young spiderlings typically leave the sac about 30 days after when the eggs were first deposited. Upon emergence they feed on mites and small insects. Of course, the spiderlings are too small to bite humans and present no hazard from that standpoint. However, they do contain a toxic material n their bodies for several days and, if accidentally consumed by a child or dog, the possibility of poisoning does exist. The life cycle is completed in 4 to 6 months with the adults surviving an additional several months. These spiders can be found in many situations but common environment requisites include high humidity, food and dark protected locations.
As with other spiders, black widows balloon or parachute as spiderlings. They crawl up on a twig or other surface and shoot long strands of silk out of their spinnerets. Air currents pick up this webbing and carry off the attached spiderlings. With the heat of the day the floating spiderlings are carried upward as high as a couple of miles. As temperatures cool and wind turbulence decreases at night, they float back to earth. If they reach the prescribed environmental conditions they survive, if not they die. In actuality very few young survive to adulthood; however, because the female can produce as many as 2,000 or more during her lifetime, only 2 need to survive to replace the parents and perpetuate the species.
These spiders are not typically aggressive except in defense of the egg sacs. The fangs of a black widow are quite small and incapable of penetrating thick skin. Consequently, in order to inject venom, a black widow must bite humans on the soft parts of the body. The bite of this spider is rather painless at first; however, a systemic effect soon develops. The neurotoxin venom of a black widow is said to be 15 times more powerful than that of a rattlesnake. However, there is much less toxin, so the bite is normally not nearly as bad as that of the snake. Pain begins after 1 to 3 hours and continues for 24-48 hours. Pain often starts in the lymph nodes (groin, armpit) and spreads to the lower back. The stomach muscles develop severe cramps due to rigid contractions. The skin feels clammy, blood pressure drops, and profuse sweating and nausea may develop. Additional symptoms include facial muscle spasms, breathing difficulties and convulsions.
In humans, the mortality rate is approximately 5% of untreated bites by an adult female black widow. Most deaths occur in young children (more venom per body mass) or individuals who are already in poor health. The most common location where black widow bites occur in Southern California is outdoor bathrooms. The area right under the toilet seat is dark, humid and abounds with flies. So, in the springtime when the female is guarding her egg sacs and an unsuspecting human wiggles her web with soft body parts, it can be quite surprising (ouch!).
There is an antivenin available for bites. This is not always given as it can only be taken once. Frequently hospital patients are given Demerol or something else for the pain if the bite doesn’t seem to be too serious or life threatening. The antivenin is quite effective; however, it is not always advisable to use this on all patients as some may develop an allergic reaction.
Black widow antivenin is produced by a fairly complicated procedure. There are a number of small companies that raise black widows by the thousands. Applying a mild electrical shock stimulates the female spider to exude a tiny drop of venom from each fang. Subsequently, this venom is collected with small capillary tubes and saved. The venom from each company is pooled in the U.S. to make the antivenin. This is accomplished by injecting small amounts of the venom into horses that possess a degree of natural immunity to this toxin. After a few weeks when the horses have developed even more immunity as a result of exposure to the venom, serum is condensed from their blood to make the antivenin.
As previously mentioned, occasionally individuals treated with antivenin will develop allergic reactions. One such reaction is to develop hives and other symptoms when eating beef. Apparently, at least some of the protein in beef is the same or similar to that in horse blood serum. As a consequence, an allergic reaction unfolds in some cases when beef is consumed.
The brown widow spider, a close relative of the black widow, has recently received considerable attention and has been accidentally introduced Orange County, California and other parts of the country. Although belonging to the same genus as the latter the bite of the brown widow typically results in some pain and swelling but lacks the other symptoms from the bite of the black widow. These spiders are very similar in appearance to the black widow but differ in that their legs bear a degree of striping. More strikingly the surface of the brown widow egg sac is distinct spiked (Figure 7) where that of the black widow is rounded in appearance with a smooth surface.
Figure 7. A brown widow spider with distinctive egg sac.
It should be mentioned that in California and possibly other western states, there is a species of spider that looks very similar to the black widow, but does not have the toxic bite. This is the comb-footed spider (Figure 8). It is found in similar situations as the black widow, has an asymmetrical web and the females of both species are about the same size; however, the web of the former is weak unlike that of the black widow. Also this spider lacks the red marking on the underside of the abdomen.
Figure 8. A comb footed spider-similar in appearance to black widow.
Recluse, Violin or Fiddle Back Spiders
Spiders in the genus Loxoceles belong to a unique family known as the six-eyed sicariid spiders. These spiders all have 6 eyes (rather than the normal 8) that are arranged in a horseshoe pattern in 3 clusters of 2 eyes each. The family not only contains the genus Loxoceles, but also the six-eye crab spiders (genus Sicarius) of Central and South America and South Africa (discussed later). This is the first group of spiders that were discoved to cause the condition known as necrotic arachnidism. This term refers to the main symptom caused by a bite of these spiders, namely rotting of the flesh. A physician in 1872 associated this symptom with the bite of the Chilean recluse spider. Up to that point the condition was referred to as gangrenous spot. In the US it wasn’t until 1957 that necrotic arachnidism was associated with the bite of the brown recluse spider.
At least 56 species of the recluse spiders have been identified, 54 of which occur in the Americas. Outdoors these species typically are found beneath fallen debris and rocks. They also do well indoors and typical locations include but are not limited to behind picture frames, in fold of clothing, boxes and shoes. Storage areas are common locations where the spiders are least disturbed. Most recluse spiders are rather timid and are reluctant to bite unless disturbed and do so in defense.
In the United States there are 11 native species of recluse spider and 2 imports from South America. The most notable of these are the brown recluse, Loxoceles reclusa (Figure 9), which is commonly found in the central and south-central states and Loxoceles laeta or the Chilean brown spider (also known as the South American violin) which was found in Los Angeles a number of years ago. Recent identifications are non-existent. The brown recluse was once established in California but there is also considerable controversy as to whether or not it still exists here. The medical community annually reports treating many bites from the recluse spider. However, spider experts claim this spider no longer exists in California. Because little is known about the effect of the bite of many spider species, it is quite probable that these medically treated cases are not due to the recluse but any of a number of other spiders or, in many cases, are not due to the bite of any spider at all.
Symptom of recluse spider bite.
The brown recluse, violin or fiddleback spider. Images courtesy of CDC.
The adult brown recluse (also known as the fiddle back spider or violin spider) is a small-to-medium sized (1/2-inch body length) spider that is yellow to brown in color with distinctive violin shape markings on the cephalothorax. The appearance of the violin marking is not sufficient to identify this spider. There are other common spiders with similar markings. The six-eyes plus the marking are more useful. The web is medium sized, irregular in shape with thick strands and is not typically used to trap insects but rather more as a retreat.
Both the males and females are dangerous. The symptoms of the bite of this spider are quite similar to those discussed with the hobo spider. The venom causes a local, necrotic reaction. The victim may not feel any pain for 2 or 3 hours after the bite or a painful reaction may occur immediately. In this case a stinging sensation is usually followed by intense pain. A blister forms as well as a painful, reddish margin. The tissue at the center of the bite becomes necrotic (Figure 11) and involves the skin as well as subcutaneous tissue. In some cases the necrosis continues to increase resulting in a huge open sore that can reach several inches in diameter. The healing is very slow (up to several months) and often leaves an extensive scar (Figure 10-11).
Systemic effects are not too common to this species, but may include chills, nausea, fever, muscle pain and other flu-like symptoms. In severe cases convulsions may occur along with abnormalities in the clotting of the blood. Damage to the red blood cell walls, resulting in leakage of hemoglobin, occurs in some cases. This can result in death due to renal failure as the kidneys attempt of deal with the damage red blood cells. There is no antivenin available, but the bite is often treated with corticosteroids and excision of the bite area. In advanced cases the lesion may become so large that amputation of limbs may be necessary.
Figure 10. Symptoms of brown recluse spider bite after different time periods-few days after bite. Image courtesy of Center for Disease Control.
Figure 11. Scar from brown recluse bite. Image courtesy of Center for Disease Control.
Loxoceles laeta, know as the Chilean brown spider, also prefers tight places in buildings. The bite of this spider is partially systemic and sometimes fatal. Internal bleeding often affects the kidneys and liver. Unfortunately, 50% of children bitten in South America die without treatment. Antivenin is available in South America. The bite’s progress is slightly different from the recluse in that the ulcerated area is dark rather than white. This spider is a nocturnal hunting spider that searches for prey away from its web.
The desert recluse spider (Loxoceles deserta) is another relative of the more notorious brown recluse, or violin spider. The distribution of this species in California is quite limited, occurring in isolated desert areas above 3,000 feet elevation. This is a medium sized non-descript tan species with many fine hairs covering the body. Very few people are bitten by this species and the symptoms are similar to, but far less severe than, that of its cousins.
Very little is known about the bite or symptoms of the other recluse spiders that are found in the United States. The distribution of these as is follows:
- The Tucson recluse, Loxoceles Sabina. Limited to Tuscon area.
- The Arizona recluse, Loxoceles arizonica. Central and southern Arizona and SE California.
- The Baja recluse, Loxoceles palma. Baja and S.California.
- The Big Bend recluse, Loxoceles blanchi. Western Texas.
- The Grand Canyon recluse, Loxoceles kaiba. Grand Canyon.
- Matha’s recluse, Loxoceles martha.
- The Mediterranean recluse, Loxoceles rufescens. Introduced species, several US cities. Bite not considered as toxic as some of the other species.
- Russell’s recluse, Loxoceles russelli. Death Valley.
- The Texas recluse, Loxoceles devia. Texas.
- The Tucson recluse, Loxoceles sabina. Tucson area.
The hobo spider (Figure 12) is found primarily in the Pacific Northwest. This spider was introduced from Europe into Seattle in the 1920’s and since that time its distribution has expanded over to Montana, down into central Utah and northward to the Alaskan panhandle. This spider creates funnel shaped webs in woodpiles and crawl spaces of buildings and is moderately large in size and brown with gray markings. They are quite fast and can move up to speeds of one meter per second. They do not crawl up walls so distribution in the home is normally limited to the basement or a floor level.
The bite of a hobo or aggressive house spider does not necessarily result in many symptoms other than the initial prick. As with many other venomous critters, the bite can occur both as a dry bite where no toxin is injected and as a wet bite where toxin is injected. With the hobo spider in approximately 50% of the time no toxin is injected which is typically associated with a defensive reaction. Toxin is frequently injected and associated with subduing prey. Typically defensive bites of the hobo spider are lightning fast with the spider striking and then rapidly withdrawing. Very often the initial bite is painless although this varies depending on the location and psychological reaction of the victim. Spider bites in general and those of the hobo spider tend to be singular in nature (unlike those of some other arthropods). However, multiple bites do occur, especially when the spider is trapped between clothing and the skin and cannot escape.
The symptoms of a bite when toxin is injected are similar to those of the recluse spiders and in extreme cases can be quite painful, debilitating and, in rare cases, deadly. The severity of the symptoms depends to a degree on the age of the victim and sex of the spider. Indications are that the bite of a male spider is more toxic than that of the female and small children and elderly people are most susceptible. Also symptoms vary depending on how much toxin is injected and the victim’s reaction to the toxin. Bites from this spider are reported to be on the increase in the northwest. Undoubtedly there are many more bites than recorded as spider bites are not required to be reported to the disease monitoring authorities.
Typically, within a few minutes after the bite, a large (several cm.) reddened area develops at the site. This normally disappears within a few hours leaving a smaller hardened area that appears similar to a mosquito bite. Within a day or two a blister may form which subsequently rupture, leaving an ulcer. The ulcer normally scabs over and within 3 weeks of the bite, becomes pronounced, looking somewhat like a “target,” which is referred to as the bulls eye effect (Figure 13). Following this the scab is sloughed off leaving a scar and healing is completed within 45 days of the initial bite.
Systemic or generalized effects are seen in about 45% of individuals bitten by hobo spiders. The most common of these symptoms is severe headaches that normally do not respond to standard painkillers. Other symptoms include nausea, dizziness, hallucination, dry mouth, visual disturbances, joint pain and lethargy. About 15% of bite cases require hospitalization.
Below are 3 case reported by the CPCD. Case 1 (a 10 year old boy) developed 2 lesions (hot, swollen, red and blistered) within 48 hours of having been bitten. Systemic symptoms included fever, nausea, and severe headaches. In 7 days necrosis and skin sloughing developed. Migraine headaches occurred for 4 months. Case 2 (a 42-year-old woman) had a severe headache, nausea, and dizziness within 3 hour of the bite, which was followed by the appearance of a lesion with a vesicular center. The vesicle ruptured the next day leaving an open lesion that expanded in size for the next 7 months. After 13 months the lesion healed leaving a large scar. A venogram was taken 10 months after the bite that revealed deep venous thrombosis (inflammation of the veins), which did not respond to treatment. The patient remained unable to work, where she had to stand or walk. Case 3 (a 56-year-old woman) developed aplastic anemia, and several other symptoms and died 2 week after the bite from internal hemorrhaging. Treatment for hobo spider bites is not well defined. The CDCP suggest applying heat and ice to the site, diphenhydramine for allergic response and antibiotics for secondary infection.
Figure 12. A hobo spider.
Figure 13. Necrotic lesion due to hobo spider bite. Image courtesy of Darwin Vest.
Yellow Sac Spider
Yellow sac spiders (Figure 14) are one of the least know of the medically important spiders. There are 3 species that are widely distributed in the United States, namely Cheriacanthium inclusum, C. mildei and C. mordax. In many other areas of the world species in this genus are well document for their toxic bites. These spiders build their lair, which appears as sac-like silken tube in vegetation, or under objects; however, they occasionally enter homes, restaurants, automobiles or other structures. These spiders are relatively small (10mm body length) and are yellow in color.
Figure 14. A male yellow sac spider adult. Image courtesy of Lisa Ames, Univ.Georgia-Bugwood.
These spiders are prone to bite defensively (more so than other significantly venomous spiders). The yellow sac is capable of causing a painful bite, which typically results in tissue necrosis and possibly systemic effects. Normally this necrosis is not as severe as that produced by the hobo or recluse spiders. The bite of this spider typically produces an instant pain much like that of a bee or scorpion sting. A reddening of the skin, swelling and itching, usually follows. Necrosis may or may not develop, but when a necrotic lesion does develop it heals within 8 weeks or less. If low-level systemic effects develop, they are typically not diagnostic and include dizziness, chills, fever, nausea, anorexia and shock. Treatment is the same as that used for the recluse or hobo spiders.
It is likely that many U.S. cases of necrotic spider bites that have been attributed to the brown recluse spider were actually yellow sac spiders. C. mildei was first identified as a cause of necrotic spider bites in 1970 in the Boston, Massachusetts’s area where it is the most common spider found in homes. It is also common in homes in New York City and may be the source of recent rumors of infestations of the brown recluse in that city.
Most Dangerous Spiders in the World
The Sydney funnel web spider (Figure 15) is reported to be one of, if not the most, deadly spiders in the world. This Australian spider has gained the reputation of being extremely aggressive. When confronted, the spider will rise up on its hind legs, lunge forward and bite repeatedly if given the chance. The fangs are large, powerful and capable of penetrating a fingernail. The venom of the smaller male is several times more toxic than the female’s. This is unfortunate because the males tend to leave their burrows and roam freely, especially following heavy rains. As might be expected this spider gets its name from the fact that it occurs around the Sydney area and has a funnel shaped web (Figure 16).
Following a bite from this spider, symptoms develop quite rapidly; these include nausea, vomiting, heavy sweating, and finally, collapse. Unbearable cramps develop along with severe pain in the limbs. The lungs become quickly filled with fluids, causing cyanosis (turning blue) due to the lack of available oxygen. The victim eventually convulses and lapses into a coma, frequently dying, especially if very young. Fortunately, a very successful antivenin has been developed.
Figure 15. A Sydney funnel web spider. One of the world’s most dangerous spiders. Image courtesy of Queensland Museum.
Figure 16. The characteristic web shape of the Sydney funnel web spider. Image courtesy of Queensland Museum.
The Six-eyed Crab or Sand, Spider
This spider belongs to the genus Siciarius, which is a South African living fossil that pre-dates the Gondwanaland drift some 100 million years ago. Also occurring in South America, these are large spiders approaching 2 inches in length with a leg span of 4 inches. This is a flattened species, which spends much of its time buried beneath the surface of the sand waiting for a potential meal. To bury itself, it raises its body, digs a hole, drops in and then covers itself in sand with its front legs (Figure 17).
Sicarius hahni from the Northern Cape is possibly the most lethal species of spider in the world. Fortunately, due to its habitat, it is rarely encountered and appears reluctant to bite. Less fortunately there is no antivenin for a bite, making the bite much more hazardous than that of the Sydney funnel web where an antivenin is available.
Figure 17. Six-eyed crab spider above sand. Image courtesy of Museum of Cape Town.
Figure 17. Six-eyed crab spider below sand. Image courtesy of Museum of Cape Town.
The Brazilian Wandering Spider
This spider is regarded by some as the most dangerous spider in the world. It is highly venomous, very fast and aggressive. However, recent studies indicate that these spiders only inject venom in about one-third of their bites and may only inject a small amount in another third. Thus the effects of the bites from these spiders can range from only a couple of pin pricks to a full-blown problem. The Sydney funnel web spider apparently injects venom in every bite and may thus in effect be more dangerous- although either spider’s venom can lead to a medical emergency.
The Brazilian wandering spider is reputed to occasionally hide in clusters of bananas. As a result, any large spider appearing in a bunch of bananas should be treated with care. This spider should not be confused with the “other” banana spider or Huntsman spider that is discussed later in the text. It is called the wandering spider because it wanders the jungle floor, rather than residing in a lair or maintaining a web.
Not Dangerous but Occassionaly bite
One of the most notorious groups of spiders is the tarantula (Figure 18). Because of their large size, Hollywood and the motion picture industry have exploited these spiders. In the movies, when a tarantula bites someone, the typical reaction is immediate death. Actually most tarantulas are docile, reluctant to bite and make nice pets. There are very few species considered dangerous to humans. The bite of the average tarantula worldwide is no worse than a bee sting. Generally speaking, the larger the tarantula, the more venom is injected. Thus, although often undocumented, the bite of some of the giant South American species could cause considerable pain, swelling and tissue degeneration in humans. The bite of any tarantula generally results in a deep puncture wound due to the relatively large fangs (Figure 19) and should be treated with a tetanus shot.
The origin of the name tarantula has an interesting history. The name was originally given to a species of spider that commonly occurred around the Italian city of Taranto. Because of the large size (1 inch is large for a European spider) this species was greatly feared. During the Middle Ages it was believed that if someone was bitten by this spider the only cure was for the patient to dance wildly until he or she fell down out of exhaustion. As a result a very vigorous dance in the region was given the name tarantella. In addition a group of musicians traveled around the countryside that was more than willing to assist in treatment of spider bites. It is now documented that the fear of this original tarantula was unfounded since the bite of this spider is no worse than a bee sting.
It is probably not a good idea to handle a pet tarantula as these are basically wild animals and can be unpredictable in behavior. A case in point was recently demonstrated with my wife (Pat) and coauthor of this text. She used to do classroom presentations and frequently used a rather docile species of tarantula to show the kids. Unfortunately one day she accidentally dropped the critter. Well tarantulas are rather heavy bodied and do not fall well. If the exoskeleton of a tarantula is cracked the animal will usually bleed to death as its blood flows freely within the body and is not contained in vessels. Needless to say the tarantula died. By the way I recently learned that if you drop your tarantula and crack its exoskeleton without causing internal damage, superglue can be use to seal the crack and save the spider. Anyway we were looking for a replacement and someone gave me a Chilean rose haired tarantula which has a reputation of being very docile. Well Pat asked me to hand her the tarantula but once placed on her hand it sunk its fangs into her thumb. She was quite calm about it and merely stated “I think you should remove the spider as it is biting me”. I had told Pat that the bite of a tarantula is no worse than a bee sting which is true but I did not tell her that we didn’t know a lot about the effects of the venom of all tarantulas. She actually did have some unusual effects. One of her arms went numb which subsequently progressed to her back and across to the other arm. Even today she has 2 small pits in her thumb as a result of the spider’s injected venom in an attempt to digest her (see external digestion).
Tarantulas are long lived. The females of some species can live upwards of 20 or more years. On the other hand the males rarely live over a few years. Part of the reason for this is that males reach sexual maturity within 3 to 4 years on an average. At that point they search for a female and if successful are consumed by their mate after mating. If they escape from the female they soon die as their biological function is finished. It is thought that the male may actually hang around after mating and make no attempt to escape. This is advantageous to the species as the female has a tasty meal in preparation to egg production. Male tarantulas differ structurally from females in that their bodies are less bulky with long legs; many have bulblike structures on the tip of their pedipalps for sperm transfer. Hooks on some male’s front legs are used to hold the female’s fangs so she can’t eat him during mating.
Figure 18. A nicely marked species of South American tarantula.
Figure 19. The chelicerae or fangs of an average sized tarantula.
Besides biting, New World tarantulas frequently protect themselves by kicking off puffs of branched body hairs from the back of their abdomens with their hind legs (Figure 20). The mucous membrane of the eyes and nose of mammals, including humans, are quite sensitive to these hairs and resultant watery eyes and severe itching of the skin may last for several hours. These hairs can penetrate the skin up to 1/16 inch and frequently have a toxin associated with them. People who handle tarantulas may develop an allergic reaction to this venom, causing increased sensitivity and irritation after minimal contact. Because the venom in the hairs is likely to be the same as that in the fangs, someone who has developed sensitivity to the hairs could have a more severe reaction upon being bitten. The hairs are regenerated each time the tarantula molts.
Figure 20. A South American goliath tarantula with balding abdomen due to defensive kicking of hairs.
Most tarantulas in the United States feed on insects and, possibly young rodents. There are a number of tropical species that live in trees (arboreal) and possibly feed on young birds (the bird spiders). Many of the bird spiders are relatively slender bodied and exceedingly hairy with long hairs extending at right angles from the body. The authors were not sure of the function of these hairs until one day we accidentally dropped a rather hairy one. While in midair, the spider extended its legs in all directions and floated to the ground--much like a falling leaf. The long hairs obviously increased the surface area of the spider, which along with the spider’s relatively light body, allowed it to perform this acrobatic feat--a behavior that obviously has advantages when living in trees. The main diet of bird spiders is not birds but insects.
The Mexican red-knee (Figure 22) is one of the most brightly colored and docile tarantulas known. This species was collected by the thousands from Southern Mexico and imported for years into the United States for the pet trade. Several years ago the Mexican government prohibited this practice due to the depletion of the species. Mexican red-kneed tarantulas occasionally can still be found in pet stores but these come from tarantula breeders. They are typically available as tiny spiderlings.
The importation and exportation of animals and plants and/or their parts (e.g., Mexican red-knee, animal horns, and spotted cats) in many countries throughout the world has become a major problem. As a result, a number of these countries have formed an international agreement called the Cites Agreement. . Each country has identified the plants and animals (including their parts) which they want to protect. Once placed on a CITES list, an organism cannot be exported from a country without a permit from that country. In many cases these permits are not available. In the United States, the Fish and Wildlife Services enforces this agreement. If they catch someone exporting or importing an illegal CITES organism, the penalties can be quite severe. An individual recently was caught bringing into the U.S about 80 Mexican red-knee tarantulas. He was sentenced to 6 years in jail.
In the news today (August, 06) there was a case where an individual was caught trying to import a number of illegal butterflies (CITES ) including 2 Queen Alexander birdwings-largest butterflies in the world-valued at $8500 each. He was indicted on 15 Federal charges as a result of a 3-year investigation by the Federal Fish and Wild Life Services. This individual was a fairly well-known insect dealer.
Figure 22. A female red knee tarantula.
The authors were somewhat skeptical about reports of a few incidences where a tarantula attempted to heal its own wounds with its webbing. However, one day we were closing the cage door of a Chilean rose-haired tarantula and accidentally chopped off part of its leg. As blood began to ooze from the wound the tarantula spun several strands of silk and wrapped it around the wound, thus effectively sealing it. Without this tourniquet the tarantula would likely have bled to death. The Chilean rose-haired tarantula (Figure 23) is the most common species sold in pet stores. They tend to be quite docile and in most cases are reluctant to bite.
Figure 23. A Chilean rose-haired tarantula-the most common species available in pet stores.
The goliath spider from South America (Figure 24) is the largest species of spider in the world. A large specimen with its legs fully spread will exceed the size of a dinner plate (10 inches). Some of these giants of South America feed almost exclusively on lizards, frogs and snakes. This spider is commonly referred to as a bird eater. This is a misnomer as these ground inhabiting, heavy bodied spiders are rather slow moving and can not climb all characteristic which would be detrimental to catching birds. Apparently this name was probably acquired because one of the original books published about spiders had a drawing of this spider sitting next to a dead bird. When given a choice this tarantula prefers the cold-blooded vertebrates to insects. Some of the more primitive human tribes actively seek these giant tarantulas of the rainforest as a food source; the spiders are roasted to remove the body hair. The eggs of a gravid female are a special treat making a nice omelet! Tarantula is said to taste like chicken; actually, it has a distinctive flavor of its own-I guess.
On one occasion we received a live adult female goliath spider. As one of my colleagues and I were observing the spider, I asked him, "Do you want to hold it?" He responded rather abruptly, "No!" I replied, "Me neither, let’s feed it." It was a real monster, with at least one-inch long curved fangs. So we proceeded to throw a large mouse in its cage. The spider immediately jumped on the mouse and began pumping in salivary enzymes with its needle shaped fangs. Upon our return the next day, there was nothing left but a small ball of fur. The tarantula had consumed, everything else including the bones. We never handled that one-Ever.
Figure 24. A Goliath spider-one of the largest tarantulas in the world.
Other Spiders that bite
All spiders have fangs and poison glands (there are a few exceptions); however, many are timid and will not or cannot penetrate the skin because their fangs are too small. There is a tremendous lack of knowledge about the effect of the bite of many common spiders in the world. A good example of this is the brown recluse. As mentioned above, the spider experts strongly feel that this spider no longer exists in California. However, as with many other hospitals, Redlands Community (a Southern California hospital) reports treating several brown recluse bites a year. If the spider experts are correct, there must other species of which we are not aware, whose bite produces symptoms similar to that of the brown recluse.
A few species of jumping spiders are reportedly very aggressive and on occasion bite humans. The venom is not very potent and the bite is initially painful leaving 2 small red marks that heal in a few days. Johnson’s jumping (Figure 25) spider is the most common species that has been reported to bite humans. This outdoor species is nearly 1/2 inch long (big for a jumping spider) and has a black head with a black and red body.
Figure 25. Johnson’s jumping spider has a painful but not dangerous bite.
These are some of the most readily recognized and common spiders found in the US as well as in the tropical areas of the world (over 4,000 species worldwide). They are readily recognized by their distinctive shape and ability to jump (Figure 26). These spiders are capable of jumping over 40 times their length. This is equivalent to a 6 foot man jumping 240 feet. Whenever we go to elementary schools to give a presentation and show a slide of a jumping spider, most of the kids already know exactly what it is.
An additional distinctive characteristic is their large eyes. These spiders have the best-developed visual system of all spiders, which is used to best advantage when hunting prey. As do most spiders, they have 4 pairs of eyes. One large pair and 1 small pair are oriented in a forward facing position. Above this front row is a second row of 2 tiny eyes and behind these there is a set of 2 large eyes oriented in an upward position. As a result these spiders can see in a 360-degree plane. Unlike other spiders they can move their eyes outward or inwards for focusing and they can be turned up and down and from left and right. The spider can also turn its carapace (breast) more than 45 degrees to look around.
Figure 26. Jumping spiders with well-developed eyes. Top images courtesy Peter Chew, Brisbane Insects.
Figure 26. Jumping spiders with well-developed eyes.Image courtesy Peter Chew, Brisbane Insects.
Figure 26. Jumping spiders with well-developed eyes.Image courtesy Peter Chew, Brisbane Insects.
Figure 26. Jumping spiders with well-developed eyes.Image courtesy Peter Chew, Brisbane Insects.
Figure 26. Jumping spiders with well-developed eyes.
Prey can be distinguished from a distance of about 30-40 cm. Experiments have indicated that they are capable of distinguishing dangerous insects from prey. As their name implies, jumping spiders do not use webbing to capture their prey. Anyone who has ever watched these tigers of the spider world stalk their prey is truly amazed. They typically edge up until they are within an inch or so of the prey and then pounce. They are capable of subduing prey that is many times their size. When one of these spiders jumps, it simultaneously releases a silken lifeline. If the jump fails it can then crawl back to its original position. As indicated jumping spiders do not make webs to catch prey. However, they do make a retreat of thick, white, slightly viscous silk which typically occurs in crevices, under stones on the ground and similar situations.
These spiders live for the most part on vegetation. However, some species exhibit an amazing resemblance to ants and are called ant-like spiders. The obvious advantage of this is that they can intermingle with and feed on ants without being detected. In some cases, they have been shown to travel on the same trails with certain species of foraging ants.
This (Figure 27) is another species of common spider that reportedly bites humans. This species is a little less than 1/2-inch in length with 2 dark parallel stripes running the length of the cephalothorax. The overall body color is tan with mottled white markings. This spider inhabits gardens and junk piles and lives under stones and logs. The web is trampoline-like in shape and tapers back into a funnel where the spider hides and waits for its prey. This species can produce a painful bite due to its powerful jaw muscles and large fangs. The nature of the venom is unknown. Typically a bite will cause mild swelling and a red spot. There have been some recorded cases of more severe symptoms. These could possibly be due to allergic reactions to the venom.
Figure 27. A grass spider may bite resulting in mild swelling.
Green Lynx Spiders (Figure 28) are about 3/4 inch long and apple green in color with long spindly legs covered with black spots. This species is found in gardens, chaparral, on flower heads of wild buckwheat, in tall grass and bushes. It hunts and captures it prey without the use of a web. The green lynx fiercely guards its egg sac and is capable of biting and spitting its venom a distance of a few inches. The venom may cause eye irritation that will clear up in a few days.
Figure 28. The green lynx spider is capable of spitting its venom a few inches. Image courtesy of Russ Ottens, Univ. Georgia-Bugwood.
Spiders that rarely or never bite
Orb Web Spiders
These are some of the most obvious outdoor spiders. In the US these spiders are also called "garden spiders.” They are large, often brightly colored spiders (Figure 29) that make large webs in locations that are readily visible. An orb web is the stereotypical web that most people think of when they think of a spider web. It basically consists of 25 to 30 radial fibers that are connected by a number of spiraling or circular fibers. The spiral fibers are coated with a thin layer of sticky material that under tension breaks up into tiny globules. These are the fibers that trap the spider’s prey. The question may arise why does a spider not get trapped in its own web? One reason is that when traveling over its web it moves primarily over the radial fibers avoiding the sticky material on the spiral fibers. In addition their legs are coated with an oily material that repels the sticky substance.
Figure 29. Orb web spider.
Figure 29. Orb web spider.
Figure 29. Orb web spider.
This spider can be identified by the construction of its web. It is the only spider that makes a zigzag line or a cross of zigzag white material in the web (Figure 30). The exact function of these lines is not known; however several have been suggested. The spider hangs head down, in the hub. When stimulated the spider vibrates its web vigorously until it becomes an indistinct blur. The combined zigzag structure and indistinct appearance are thought to possible increase overall apparent size of the spider making it less attractive to potential predators. This vibrating also possibly makes the spider a less precise target to a potential predator. More recently it has been found that in some spiders these structures reflect ultra violet light. It is well known that many flowers also reflect ultra violet light which functions as guides leading to their nectar-producing glands. As a result it has been suggested that instead of functioning as a protective device against predators the stabilmentum serves to attract nectar seeking insect to the spider’s web.
Figure 30. Orb web with stabilimentum. Image courtesy Peter Chew, Brisbane Insects
Figure 30. Orb web with stabilimentum. Image courtesy Peter Chew, Brisbane Insects
These spiders have very long legs and look similar to the harvestmen or true daddy longlegs (Figure 31). The harvestmen are not true spiders and actually belong to a separate order (Phalangida), as discussed earlier. The members of the daddy-longlegs spiders (Figure 32) are the most common spiders that are found in houses and buildings. They normally make their webs in the corner of a wall or ceilings but in warm climates are also very commonly found under the eaves of homes and porch overhangs. Another common location is in basements or cellars, thus being referred to as the cellar spiders. My wife really like spiders and doesn’t want me killing these spiders that inhabit our house. Consequently we don’t have to decorate that much for Halloween. When it gets really bad I sometimes sneak out with the vacuum at night. When disturbed or under threat of attack, they violently vibrate their web in attempt to discourage the intruder, hence another common name of the vibrating spiders. Some indications are that this spider has very toxic venom; however, their fangs are too small to penetrate the skin and are not considered dangerous. (Pat’s note: Dick doesn’t know it, but I go back out and sneak them back in after he goes to sleep.) (Dick’s note. I do now!)
Figure 31. True daddy longlegs, not to be confused with daddy longleg spiders. Images courtesy of Joseph Berger, Colorado State Univ., Bugwood.
These spiders spin untidy webs that are readily abandoned if they become dirty. When webs are abandoned, the spiders immediately spin new webbing, thus accounting for the large amount of webs that can be found in a home with relatively few spiders. The main webbing is relatively weak and typically is not used to trap prey and is primarily used for retreat. Likewise their chelicerae are also too small to hold prey. This spider traps its prey by throwing tough, stiff web material over the victim. After the prey is motionless, it is wrapped and subsequently pumped full of digestive enzymes. These spiders are capable of subduing almost any type of arthropod including larger wolf spiders, black widows and even other daddy longlegs. Even though the average homeowner is unwilling to put up with them, these spiders are quite effective predators and can significantly reduce the presence of other bugs in the home.
In the winter when the general insect population is at its lowest, the spider moves through the house on hunting expeditions. On such occasions it even starts looking for the web of other species of spiders. If found it will vibrate the web (simulating a captured prey) in combination with acting like a captured prey-this behavior includes twitching its abdomen, bouncing in place and shivering and tensing while contracting its legs toward its body. All these behaviors tend to excite the other spider which emerges expecting a capture prey but is consumed by the larger long-legged cellar spider.
Figure 32. Daddy-longleg or cellar spider.
This species originally came from the tropics and in colder climates is found only inside houses. Unlike most other spiders, daddy longlegs breed throughout the year. The fertilized eggs are not spun in a cocoon, but are held in a small net of silk. Because the spider is always on the move, it is common to see a female carrying her sac of 20 to 30 eggs with her.
These spiders are real hunters and because they depend on vision to catch their prey, they have excellent eyesight with 8 well-developed eyes. Four small ones are located at the lower part of the front of the cephalothorax. Immediately above these there are 2 large eyes that face forward and farther back there are 2 large eyes that are directed upward. In this way the spider can look in 4 directions and can perceive a moving insect at a distance of several inches.
These are relatively large spiders with elongated legs, an adaptation for fast movement that is needed to run down their prey. These spiders vigorously attack their prey crushing them with their well-developed chelicerae. Their name "wolf spider" is derived from the fact that people erroneously thought they hunted in groups like wolves.
The spider lives in every variety of terrestrial habitats. They have been found skating over water and even diving under the surface, catching small fish and insects. Some of these spiders fish by placing and wiggling one of their legs in water. If a fish is attracted, expecting to catch a meal, the spider quickly attacks it.
Unlike most other spiders, the majority of the wolf spider species show a degree of maternal instinct by carrying their egg sacs attached to the underside of the abdomen. Once hatched the spiderlings crawl on the back of the abdomen until the first molt. During that time the mother will engage her normal hunting activities with her young tightly attached to her body (Figure 33). When the young are brushed from her body they will crawl back very quickly. During the time the young are attached at the body of their mother they do not eat living off of stored nutrients in the bodies. During this time the spiderlings do drink water during from morning dew.
Figure 33. A wolf spider. Image courtesy of Whitney Crenshaw, Univ. Georgia-Bugwood.
She is very protective of both the eggs and young spiderlings and will readily attack any threatening intruder. It should be mentioned that maternal instinct in arthropods in general is merely a thoughtless mechanical response to external stimuli. If the egg sac of a wolf spider is removed and replaced with a piece of cork, the female will also protect the cork with her life-no thought processes here.
Domestic Funnel-Web Spiders
The common name of these spiders is ’funnel weavers’ (Figure 34), although they are also called ‘cobweb’ and grass spiders. Because many other spiders are similar in appearance to them, these spiders are most easily distinguished by the shape of their webs rather than the spiders themselves. They weave a tubular funnel, which is used as a retreat and is located at one the silken sheet of the web. Any prey that lands on the sheet is caught and consumed in the retreat. The egg sac is found in the funnel and the male often stays with the female, which is rare in arthropods and becoming somewhat rare in human marriages. As the second common name suggests, they can be found in tall grass. These spiders occasionally enter homes. This is certainly not their normal habitat and typically results from the males wandering and looking for a female and blundering into the structure. The human female they find there is usually not so happy to see them.
Figure 34. A common funnel web, cobweb or grass spider. Image courtesy of Joseph Berger-Bugwood.
This is a large family with more than 3000 known species. They can be readily recognized by their behavior and overall appearance. They are named after the behavior of moving sideways (like a crab) when disturbed. Crab spiders are frequently brightly colored with a pancake-shaped abdomen and stout cephalothorax (Figure 35). The front 2 legs, which are often larger and stronger than the other 6, are held sideways in an open position ready to catch the prey. Their eyesight is excellent with 2 big front eyes. Sexual dimorphism, or when the male and female of a species appear distinctly different, is quite distinct in many species of crab spiders.
Figure 35. Crab spider in typical ambush position. Image courtesy of Whitney Crenshaw, Coloroado State Univ., Bugwood.
Figure 35. Crab spiders in typical ambush position; male on top of female illustrating degree of sexual dimorphism. Image courtesy of Whitney Crenshaw, Coloroado State Univ., Bugwood.
They are not active hunters and typically lie in wait for approaching meals. Favorite waiting locations include flower heads and leaves. In the case of flower heads, they mainly feed on those insects that come for the pollen and nectar. In most cases crab spiders sit on flowers of their same or similar color, relying on camouflage and the advantage of surprise. A few species can actually change their color to the surrounding environment, although unlike some other animals, this takes a few days. They remain motionless until an insect arrives and then subdue it with their legs and fangs. Often the crab spider remains for days, even weeks at the same spot.
Trap Door Spiders
These relatively large spiders (adults reaching 2.5 to 3.5 cm in length) are rarely seen as they spend the majority of their lives in well-designed tunnels in the ground (Figure 36). The only time that a trap door spider is commonly seen is when the male reaches sexual maturity and strikes out in search of a female. Otherwise they remain, grow and molt inside their tunnels. The entrance of the tunnel is typically covered by an earthen door that is hinged at one end. The door is extremely difficult to spot as it blends in with the surrounding environment.
Figure 36. A trap door spider.
Trap door spiders do not leave their burrows to hunt but merely wait with the door partially open for passing prey. Their eyesight is not well developed and they rely on sensitive hairs on their legs to pick up the vibrations of a passing prey. Some species actually place elongated twig or silken strands (Figure 37) radiating out from the entrance to increase the distance of detection from the entrance.
Figure 37. The door of a trap door spider with silken stands and twigs radiating outward to detect potential prey.
The burrow and door serve not only as a home and means to capture prey, but also protects the spiders from rain, regulates the humidity and temperature, and helps protect them from potential predators, such as centipedes, scorpions and parasitic wasps. In some species the spider has a set of spines on its legs, which it presses into the side of the burrow while it holds the door shut with its fangs. We once tried to pry open the door of one of these spiders with a spoon and actually bent the handle in doing so. It is now known that this spider can withstand the pull of 38 times its weight.
Some species store the remains of their prey and other debris behind the silk lining of the tunnel. If a potential predator breaks into the tunnel, the spider will rush to the bottom of the tunnel while simultaneously releasing the debris and silk lining, thus forming a false bottom to the tunnel and concealing the spider beneath.
These spider as their name implies are commonly found around slow moving streams or lakes, They are typically long legged (Figure 38) and are capable of rapidly running over the surface of water. Their long legs that are covered with non-wettable hairs or setae and light body allows them to accomplish this task. They either feed on terrestrial insects or are capable of diving below surface to catch aquatic insects, tadpoles or small fish. Some species will actually dip or tangle a leg into the water which is thought to either attract the above or possibly detect subsurface movement by a potential prey.
Figure 38. Common water spider. Image courtesy of Peter Chew.
Figure 38. Water spider denting water but not breaking surface tension due to non-wetable hairs on legs. Image courtesy of Peter Chew.
As grousome as these creature appear (Figure 38A) I am sure there are very few if any recorded human bites from these spiders. However based on the large size of their chelicerae they are probably capable of inflicting some type of a bite. The large chelicerae reflect their chief prey, namely wood lice or sow and pillbugs both of which have a hard exosleleton.
Figure 38A. A female wood louse spider. Image courtesy Joseph Berger, Bugwood.
Tropical Spiders of Interest
Golden Web Spiders.
Anyone who has been in the tropics (east and west) has undoubtedly come across the golden web spiders in the genus Nephila (Figure 39). These are beautiful monsters. The adult females of some species can reach a body length of 2-1/2 with a leg span of 8 inches. They are quite beautiful with many iridescent colors. In comparison to the females, the males are minute, in some species 1,000 times smaller than the female (Figure 39). The males are normally found in the same web as the female, but are not in danger of being eaten because they are so small that the female does not recognize them as food.
Figure 39. A typical (Thai) golden orb web spiders. The web of this spider is so strong that it can trap birds and bats.
Figure 39. A typical (Thai) golden orb web spiders. The web of this spider is so strong that it can trap birds and bats.
As amazing as are these spider, their web is even more impressive. The silk itself is a golden color and quite strong. The silk is so strong that birds, bats and lizards are frequently trapped and consumed. The webs themselves are large, with the central hub of the web reaching 6 to 7 feet in diameter width and the radiating supporting strands attach as much as 20 feet apart. The webs are so extensive that these spiders typically do not make new webs but continuously repair the old one. The webbing of these spiders is so strong that the natives in some of the Pacific island use it for fishing line.
As impressive as these spiders are they are not impervious to competition or even predation from other spiders. On one of our student trips to Thailand I was walking along a trail in the mountains and came across a large female Nephila spider that had recently caught and was feeding on a small bird. I noticed that there were 2 other spiders (about 1/20th her size) feeding on the same bird. Apparently there are a number of other spiders that “pirate” feed on the prey of this species. Argyrodes, a close relative of the black widow, is one of the main spiders that exhibit this behavior. This spider typically builds its web close to that of the golden web spiders but makes frequent excursions onto the web of the giant. Once this pirate determines that Nephila has made a catch it waits until the prey is subdued, tightly wrapped with the giants silk and moved to a storage location on the web. At that point Argyrodes carefully moves toward the prey avoiding vibrating her web so not to end up as desert. Once locating the prey Argyrodes cuts the filaments that support the wrapped package and steals away with its prize. The orb spider’s web is so large that it is not uncommon for up to 40 of these pirates to feed off its catch. If pickings are slime these pirates on occasion will attack, subdue and eat the orb spider.
Banana or Huntsman Spiders
This is a group of rather large (1-inch body length) tropical spiders that are worldwide in distribution (Figure 40). They got the name “banana spiders” because they are commonly found in bunches of bananas and are consequently shipped around the world. Most produce managers of grocery stores are familiar with these spiders. They are quite docile and we understand that this was the main spider that was used in producing the movie Arachnophobia.
Figure 40. Giant huntsman or banana spider.
This group of spiders (Figure 41) has a rather unique means of catching their prey. They are part of a tribe of the orb-weaving spider family (Araneidae) that no longer build an orb web, but instead attract their prey (male moths) by chemical mimicry. The moths are captured using a "bolas" which is a sticky ball of glue attached to a strand of silk (Figure 42). The spider swings this around until the ball hits and sticks to the approaching moth. The moth is then reeled in by the spider and then webbed up in silk. This would be a pretty inefficient means of capturing prey if done at random. The chance of catching a moth that merely flew by would be pretty remote. However, the spider actually emits a sex pheromone that mimics that produced by female moths to attract males for mating. Instead of finding a mate the males end up as dinner for the bolas spider. Even more amazing this spider feeds on 2 different species of moths each of which fly and typically mate at different times of the night-one early in the evening and another late at night. Accordingly the bolas spider produces and releases 2 different pheromones each at the correct time that correspond to when each species flies.
Figure 41. An Australian female bolas spider. Image courtesy of Dave Britton.
Figure 42. An American bolas spider swinging its sticky ball. Image courtesy of Dave Britton.
An equally amazing feature of this spider is the huge size of their egg sacs. Typically several (Figure 43) of these giant are produced by the female. It is thought that she is capable of doing this due to the small amount of silk used in catching her prey.
Figure 43. A female bolas spider sitting on one of its several egg masses. Image courtesy of Dave Britton.
Web Casting Spiders
These spiders have a unique means of capturing their prey. In this case they use a preformed web, much like a fish-net. The spider typically builds the web over an area that is frequented by insects such as a broad leaf, downed tree trunk or wall. The net is not sticky but are quite flexible and can be expanded to 5 times its smallest size (Figure 44). Once the spider forms the net it move to the desired position with its suspend with a safety line head facing downward and holds the 4 corners of the net with its 4 front legs. It simultaneous holds a safety line with its last pair of legs. When a prey passes under the spider jumps down by cutting the safety line and simultaneous releasing the expanded tension of the net. The net contract and entangles the prey. Some species mark the desired target area (e.g. on a leaf below the waiting spider) with white spots. It is thought these serve to indicate the prey is in a good location for capture.
Figure 44. A web casting spider with net in relaxed condition. Images courtesy of Peter Chew, Brisbane Insects.
Figure 44. Net casting spider with web expanded or stretched by spider. Images courtesy of Peter Chew, Brisbane Insects.
Management and Control of Spiders
The first consideration in spider control is to determine whether or not the spiders are living indoors. Most of the "domestic" spiders are small in size (usually 1/4"), uniformly colored (pale yellow, tan or gray), and not hairy in appearance. The one large spider that occurs indoors is the daddy-longlegs spider. Those spiders, which are casual invaders, and which would normally reside outdoors, are usually large (1/2" or more), hairy, distinctly patterned (even brightly colored), and usually jump or run quickly.
General sanitation, both indoors and outdoors, is very important in spider control. Clean up all woodpiles, rocks, trash, compost piles, old boards, and other debris. Exercise caution when working around any materials that have been stockpiled for any length of time. All garages, cellars, crawl spaces must be kept clean and uncluttered. Control of excess moisture is also helpful. Keep crawl spaces, basements and porches as dry as possible. Plant trees and shrubs far enough away from the foundation to allow sunlight and wind to penetrate. Those spiders, which enter buildings from outdoors, do so through small cracks and crevices. Thus, the sealing or caulking of these entrances will aid in spider control. Screens, tight-fitting doors and windows will help keep spiders out. Indoors, move furniture and dust under it and behind it frequently, stored materials and wall hangings should also be treated in this manner. Do not allow objects to remain in one place too long. Vacuum up all webs. Also, because spiders are strictly carnivorous, the elimination of household insects such as cockroaches, bedbugs, ants and others will help discourage spider infestations. The best mechanical control device is the vacuum. Vacuum corners, registers and window angles often. If you choose to use an insecticide out of doors, apply diazinon 25% EC completely around foundation walls and adjacent one foot of soil. Indoors, there are a number of chemical available. Do not use diazinon indoors. Use proper precaution and follow the label instructions.