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E-408
June 2006

Spiders

John A. Jackman1, Wizzie Brown2, Kim Engler3, Mike Merchant4 Professor and Extension Entomologist1, Extension Agent IPM - Fire Ant Program2, Extension Program Specialist3, and Professor and Extension Urban Entomologist4 The Texas A&M University System

Most spiders are small, inconspicuous arachnids which are harmless to humans. Their beneficial role in keeping insect populations in check far outweighs the hazard posed by the few spiders that occasionally bite humans. Very few of the nearly 980 species of spiders recorded in Texas can hurt people. Only two groups -- recluse spiders and widow spiders are considered medically significant to humans. A few other spider groups like some house spiders, Steatoda species, and sac spiders, Cheiracanthium spp., have, in rare cases, been reported to cause painful bites.

Tarantulas, jumping spiders, wolf spiders and some other spiders worry people who mistakenly believe they are seriously poisonous. Although these spiders are often large, hairy and formidable looking, they rarely bite and at worst their bite is less harmful than a bee sting. People who are allergic to spider venom, though, may react severely to any spider bite.

Many people have a phobia of spiders. Knowing how to distinguish harmless from dangerous spiders and how to prevent and control them in the home, however, can prevent needless concern and reduce the chances of harm to humans.

Recluse spiders

Five species of recluse spiders have been recorded in Texas: Loxosceles apachea, L. blanda, L. devia, L. reclusa and L. rufescens. Although only L. reclusa and L. rufescens have been recorded as venomous to people, it is best to consider all these species as potentially dangerous.

The best known of these species, the brown recluse spider, Loxosceles reclusa, inhabits many Southern and Midwestern states. Recluse spiders are frequently found in garages, firewood piles, cluttered cellars and stored board piles. They often live around human dwellings, in bathrooms, bedrooms and closets, under furniture, behind baseboards and door facings, or in corners and crevices. Recluse spiders are most active at night when they hunt. People are sometimes bitten while asleep, apparently when rolling over on a spider while in bed. Others are bitten when putting on clothes that have hung undisturbed for a some time and where spiders are hiding.

Description and life cycle

As their name implies, recluse spiders are generally shy. They spin nondescript white or grayish webs, where they may hide during the day. They are predators of insects and other arthropods, known to wander around houses looking for prey.

While walking, their body and legs together cover an area about the size of a quarter but the body itself is only 1/4 to 1/2 inch long. Their color varies from orange yellow to dark brown.

The brown recluse's most distinguishing characteristics are its eye pattern and markings on the back. Recluse spiders have six eyes arranged in three pairs in a semicircle on the forepart of the head. Uncommon in spiders, this eye pattern helps separate recluse spiders from most other spider groups. The eyes also form the base of a violin shaped marking on the cephalothorax which is the front body region of spiders and combines the head and thorax. The neck of the "violin" forms a distinct, short median groove (see Figure 1). The violin marking may be conspicuous or blend with the background color.

    

One other group of spiders, spitting spiders in the genus Scytodes, has a similar eye arrangement. Spitting spiders have long, spindly, banded legs and a spotted pattern on top of the cephalothorax. The cephalothorax is raised like a dome in spitting spiders but nearly flat in recluse spiders. Spitting spiders are slow-moving and common in window sills and other locations around the house. They are considered harmless.

Brown recluse spiders lay one to two egg masses per year in dark, sheltered areas. Similar to those of many other spiders, brown recluse egg cases are round, about 5/8 inch (1.6 cm) in diameter, flat on the bottom and convex on top. After 24 to 36 days, an average of 50 spiderlings emerge from the egg case. Their slow development is influenced greatly by nutrition and environmental conditions.

Bite symptoms

The effects of a recluse spider bite may be immediate or delayed, depending on the amount of venom injected and the victim's sensitivity. Sometimes hardly noticed at first, the bite later causes a stinging sensation that may include intense pain. Fever, chills, nausea, weakness, restlessness and/or joint pain occur within 24 to 36 hours. The bite may produce a small blister surrounded by a large congested and swollen area. The venom usually kills the affected tissue, which gradually sloughs away and exposes underlying tissues. The edges around the wound thicken, while the exposed center fills with dense scar tissue. Healing may take six to eight weeks, often leaving a scar, depending on the amount of venom injected and the reaction of the individual.

Widow spiders

The southern black widow, Latrodectus mactans, and its relatives live across the entire United States. Other widow species found in Texas include: the western black widow, L. hesperus; the northern black widow, L. variolus; and probably the brown widow, L. geometricus. Their coloration varies considerably. For proper identification, an expert may be needed to examine mature specimens.

Widow spiders are found in protected cavities outdoors or in structures that are open to the outdoors especially where insects are common. Around homes, they may live in out-houses, garages, cellars, furniture, shrubbery, ventilators, rain spouts, gas and electric meters and other undisturbed places. Widow spiders also may be seen in cotton fields and occasionally in vegetable gardens.

Like most arachnids, widow spiders are shy and retiring. People are bitten occasionally when they accidentally disturb a hidden spider or its web. To avoid hidden spiders, disturb any area before sticking you hand in places where spiders might hide. Use a stick to remove webs under benches especially in wooded areas or under the sit in an out-house.

 

Description and life cycle

Widow spiders are typically jet black, but their color and patterning can vary considerably. Males and juveniles tend to show more color, with orange, red and white markings on the back and sides. On the underside of their rounded abdomen are two reddish triangles that may be united to form an hourglass shape. Some individuals have irregular or spot like markings; others have none at all. Adult widow spiders average 11/2 inches long and have eight eyes in two rows, a common spider pattern.

Females lay eggs in a loosely woven cup of silk. The 1/2 inch long oval egg sacs hold from 25 to 900 or more eggs, which incubate for about 20 days, depending on temperature and time of year. Spiderlings usually stay near the egg sac for a few days after they emerge, when cannibalism is prevalent. Like many spiders, surviving spiderlings disperse by "ballooning." They spin a single silk thread which is caught by the wind, which carries them to a new location. When about one third grown, they establish themselves in a protected place and build loosely woven webs.

Widow spiders usually remain in their rather coarse, irregular, tangled webs for the rest of their lives. Over time they extend their webs and capture progressively larger prey. Males eventually leave their webs to find females for mating. Contrary to popular belief, most females do not normally eat the males after mating. This habit, found in a few species of widow spiders from other areas and more common in captivity, gives the group its name.

Bite symptoms

If noticed at all, a widow spider bite may initially feel like a pin prick. Usually the bite location is indicated by a slight local swelling and two red spots surrounded by redness. The reaction may transfer throughout the body (systemically) and pain becomes intense in one to three hours, continuing for up to 48 hours. Symptoms may include tremors, nausea, vomiting, leg cramps, abdominal pain, profuse perspiration, loss of muscle tone and rise in blood pressure. The toxin can also cause breathing difficulties and sometimes unconsciousness. However, less than 5% of the reported bites from widow spiders result in human death. Other common spiders

Tarantula

Tarantulas in Texas are members of the hairy mygalomorph family in the genus Aphonopelma. These large, hairy spiders are brown to black and more than 3 inches long when full grown. Females, larger than males, have abdomens about the size of a quarter.

Tarantulas hunt at night and spend the day under rocks, in abandoned mouse burrows or in other sheltered areas. They may be seen in the evening or late at night along country roads or trails. Migrating male tarantulas may be commonly seen for a few weeks in early summer. The purpose of the migration is not completely understood, but it may occur as males seek mates.

Tarantulas are sometimes kept as pets and can become quite tame. Although they can be handled, be careful, because they can quickly become disturbed and may pierce the skin with their fangs on the chelicerae. The body hairs on the top of the abdomen in American tarantulas have barbed hairs that may irritate the skin, so take care when handling them.

Tarantulas need a constant supply of water in a flat dish into which they can lower their mouths. They eat live crickets, mealworms, caterpillars or other insects but not June beetles. Tarantulas can go for several weeks without food, sometimes refusing to eat before molting. Tarantulas can crawl up glass and escape through small openings, so they must be kept in a container with a good lid.

Jumping spiders

Jumping spiders, all of which are in the family Salticidae, are among the most interesting spider groups to watch. Jumping spiders come in many sizes and color patterns. Active hunters during the day, they have good eyesight, relying primarily on movement to locate prey. They stalk their prey before attacking in a fast leap. Jumping spiders put out a line of webbing when they jump and can sometimes be seen dangling from this silken dragline after a leap that fails.

Many jumping spiders are bold, stocky and often brightly colored. They often have conspicuous bands of black and white on their bodies or legs. Others have velvety red abdomens and some even have metallic colors on the chelicerae. Jumping spiders have eight eyes, with one large pair in the front. Like most spiders, jumping spiders are not considered hazardous to humans and are unlikely to bite unless cornered or handled.

The bold jumper, Phidippus audax, is one of the most common and conspicuous of the jumping spiders. It is black with three spots on the back of the abdomen which are orange in immatures and white in adults. Like many jumping spiders, it can be found in gardens and around homes, where it is territorial. The same spider may be seen in the same locations around a window for extended periods.

Wolf spiders

Wolf spiders hunt at night. Usually brown and black, they may have longitudinal stripes. Wolf spiders are large and often seen under lights. They can be seen at night when their eyes reflect light from a flashlight, headlamp or car headlight.

Members of the genera Rabidosa and Hogna include some of our most conspicuous wolf spiders. They form webbing only to provide daytime shelter, not to capture prey. Many wolf spider females carry their egg masses below their abdomens until after the eggs hatch. Young spiderlings cling to the mother's abdomen for a short time after hatching. Hundreds to thousands of wolf spiders may live in an average backyard, where they feed on a variety of insects and small organisms. Because they are so common, wolf spiders are one of the most common types of spiders that enter homes under gaps in doorways. Fortunately, they pose no danger to people or pets.

Orbweavers

Orb weaving spiders produce the familiar flat, ornate, circular webs usually associated with spiders. Orbweavers come in many shapes and sizes, but the brightly colored garden orbweavers, Argiope, are the largest and best known. The yellow garden spider, Argiope aurantia, is marked with yellow, black, orange or silver. The female’s body is more than 1 inch long with much longer legs. It is also known as the black and yellow garden spider and sometimes the writing spider because of a thickened interwoven section in the web's center. Male Argiope, often less than 1/4 the size of females, can sometimes be found in the same web with the female. Garden orbweavers are so named because their webs can be found in fields, on fences, around homes and in other locations. The spinybacked orbweaver, Gasteracantha cancriformis, is another distinctive orbweaver that is especially common in wooded areas. The unusual flattened, spiny body shape makes it look like a crab. Abdomen colors include white, yellow, orange or red. Orbweavers are harmless but can be a nuisance when they build large webs in places inconvenient for humans.

 

Southern house spider

The southern house spider or crevice spider, Kukulcania hibernalis, frequently enters homes and causes concern when mistaken for a recluse spider. Southern house spider females are larger and darker brown than males. Larger than recluse spiders, they have eight eyes all in one cluster, and lack the recluse's violin marking. This spider's distinctive web can be recognized by webbing radiating outward from a central lair built in a hole or cavity. Southern house spiders are common in old barns and undisturbed buildings.

 

Controlling spiders

First aid for spider bites

Relieve local swelling and pain by applying an ice pack, ammonia or alcohol directly to the bite area. In case of severe reaction, consult a doctor immediately and, if possible, take along the spider for positive identification. Specific antivenin is sometimes available to treat widow spider bites.

Tips for professionals

Produced by Agricultural Communications, The Texas A&M University System Extension publications can be found on the Web at: http://agpublications.tamu.edu Additional information about entomology can be found on the Web at: http://insects.tamu.edu.

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Issued in furtherance of Cooperative Extension Work in Agriculture and Home Economics, Acts of Congress of May 8, 1914, as amended, and June 3, 1914, in cooperation with the United States Department of Agriculture. Edward Smith, Director of Texas Cooperative Extension, The Texas A&M University System.