IPM for Spiders in Schools


Although diminutive in size, spiders have invoked fear and revulsion in humans throughout history. Because of this, they have been a source of endless fascination, the subject of numerous folktales and myths. To be certain, little Miss Muffet and the spider that frightened her are familiar to most people. Fears about spiders are largely unwarranted for they provide a great benefit to mankind by consuming vast numbers of insects in and around our homes. It is only a few species of spiders which are considered truly dangerous to humans. Therefore, it is important to be able to differentiate between relatively harmless spiders and those which should be avoided and/or controlled.

The species of spiders that cause the most concern in the home or school environment are the black widow, brown recluse, and the aggressive house/hobo spider. These spiders are potentially dangerous to humans, and bites from these spiders may cause severe reactions or even death. However, these spiders will usually only bite if provoked, and only under certain circumstances.

First Aid for Spider Bites

If possible, capture the spider so the specimen can be taken to a doctor. Proper treatment may depend on identifying the species. Even the squashed remains of the spider can be useful for identification purposes.

Wash the area around the bite, calm the victim, and consult a doctor as soon as possible. Those particularly at risk are the very young, the elderly and sick, or people with high blood pressure. Although the illness and lesions from bites of the three spiders discussed in this chapter can be serious, deaths are rare.

Avoiding Spider Bites

The three dangerous spiders described in this section have particular nesting and hiding places which are described below. If any of these spiders is common around your school, it is important to be cautious when working near these places. Gardeners and custodians should be careful about where they put their hands when doing outdoor work, and wear gloves and a long-sleeved shirt when working around woodpiles and other items stored outdoors that are likely to harbor the spiders.

Make sure students and staff can identify any dangerous spiders in your area and know their likely nesting and hiding places. Children should be taught not to tease spiders in their webs or poke at them, and to not put their hands in dark crevices without looking first. The dangers of spider bites should be explained without exaggeration to avoid unnecessary fears. Teach students and staff that the "black spiders" they see walking around are not likely to be black widows, since the females (males aren't dangerous) do not travel away from their webs.

Nesting and Hiding Places for Three Problem Spiders

Black widows like dry, undisturbed places such as lumber and rock piles, stacked pots or baskets, rodent burrows, water meters, the underside of bricks and stones and dry crawl spaces. Females stay in the web.

Brown recluse spiders prefer undisturbed places for their webs, hunt primarily at night and will take refuge in clothing and bedding; often found in unused closets and storerooms, behind furniture, and in baseboard cracks and crevices. Outside, it can be found in foundation cracks, cracks in the soil, and window wells.

Aggressive house spiders prefer dark, moist places with cracks and crevices for its funnel-shaped web; is a poor climber so is rarely seen above ground level. Males wander (especially from June through September) and sometimes become trapped in clothes, toys, bedding, or shoes. Inside, this spider is likely to be found in basements and on ground floors between stored items, in window wells, in closets, and behind furniture. Outside, it can be found in areas similar to both the black widow and brown recluse.

Removal of a Non-Dangerous Spider

For those spiders that are considered non-dangerous, it may be best just to leave them where they are found. However, if this is considered unacceptable, the spider may be removed without harming it. This may be done by inverting a container of some sort over the spider, sliding a stiff piece of paper over the mouth of the container, and then releasing the spider outside.

General Spider Management

Black Widow Spiders

Identification and Biology

All of the adult females of the three most common species of black widows in the United States (the nothern widow, Latrodectus variolus; the black widow, L. mactans; and the "western" widow, L. hesperus) are large (body size is 1/2 inch or larger). They are typically shiny black spiders with a red hourglass design on the underside of their abdomen. Because their webs are near the ground and the spiders hang upside down in the web, their distinctive marking is readily apparent. The adult male, which is not dangerous, is small and patterned with whitish streaks, bars, or dots on the top of the abdomen.

Southern Black Widow Spider

There is a red form (the red widow, L. bishopi) of this genus in the sandy, scrub pine areas of central and southeastern Florida, as well as a tropical brown widow (L. geometricus) that has become established in southern Florida.

The female black widow spider spins an irregular, tangled web, with a tunnel in the center. The webs are typically constructed in quiet, undisturbed locations that are usually, but not always, close to the ground.

The female spends her life entire life in the web and retreats into the tunnel when disturbed. Her eggs are placed in white, spherical sacs within the web. After hatching, the young spiders stay near the sac for a few hours to several days and then climb to a high point, wait for suitable air currents, and spin a silken thread so they can float on the breeze like a kite. This method of "ballooning" distributes them over a considerable distance. Once they land, the spiders begin to construct their own webs. The abdomen of a young black widow is patterned with red, white, and yellow, but has the black legs and general appearance of the adult.


Black widows are shy, retiring creatures that bite reluctantly and then only in self-defense when threatened. However, when a female is defending her egg sac, she can become quite aggressive. After the bite is inflicted, it may not initially cause pain. However, after a few minutes, the bite site becomes quite painful. Symptoms from the bite of a black widow include headache, general body ache, nausea, shortness of breath, intense muscle pain, and rigidity of the abdomen and legs. If reactions are mild, no treatment is usually administered. However, if symptoms do become severe, diazepam may be administered for muscle pain and cramps. The bite of the black widow is usually more serious for a small children and the elderly.

Detection and Monitoring

Monitor for black widows at night with a flashlight or head lamp. This is the time when they move to the center of their webs and will be most visible. When making your inspections, focus on areas that are dark and undisturbed during the day, but not necessarily close to the ground. Look in and around the following places:

Black widow webs have high tensile strength and, with little experience, can be identified by the way they "pop" when broken. An experienced pest manager can use this information to find webs during the day.

Management Options

Physical Controls

To achieve some kind of permanent control of black widow spiders, you must attempt to eliminate not only the spiders but their preferred habitats as well. If this is not accomplished, another black widow may locate the same habitat and move in. If black widows regularly build their webs in certain locations indoors, try to modify these areas by increasing the light, caulking crevices, or reducing the insect population the spiders are feeding upon. As previously mentioned, check window and door screens for holes that allow access for insects, and make sure that foods and organic wastes are stored properly to prevent insect infestations. To reduce or eliminate possible web sites outdoors, debris and litter should be removed and discarded. All crevices in foundations and walls that are child-height and wide enough to stick a finger into should be caulked closed.

Brown Recluse Spiders

Identification and Biology

Brown recluse spiders (Loxosceles spp.) are identified by their long thin legs, an oval-shaped abdomen which is light tan to dark brown color, and a very distinctive violin-shaped mark on their back. This marking gives rise to their other common name, violin spiders. Their overall size is 3/4 inch to 1 1/4 inches. The males are slightly smaller than the females.

There are many species of brown recluse spider in the United States. They are found mostly in the Midwestern and south-central states, the Southwest, and Puerto Rico. As the common name "recluse" suggests, these spiders are shy, retreating from humans when possible, and preferring dark, undisturbed places on or near the ground for web-building. Unlike the black widow, brown recluse spiders hunt for prey some distance from their webs. They usually come into contact with humans because they have taken temporary refuge in clothing or bedding. Items left lying undisturbed on the floor, such as supplies, toys, or clothing, are perfect daytime refuges for these spiders. Such objects should be shaken out thoroughly if they have been on the floor for any length of time, particularly in regions where the brown recluse is prevalent.


Brown recluse spiders avoid areas of human activity. Bites are rare and are usually the result of unused rooms suddenly being put to use, or accidental contact resulting from pressing the spider between the body and either clothing or sheets. The bites are almost always very unpleasant, producing an ulcerous wound called a necrotic lesion that turns dark within a day and takes a long time to heal. Young children, the elderly, and the infirm are most likely to be affected severely. Victims should seek medical attention, but should only allow a doctor to excise the affected tissue in extreme cases.

Detection and Monitoring

The brown recluse spider wanders at night searching for prey. It seeks dark, uninhabited areas for protection. Brown recluse spiders are usually found on floors and baseboards. Only rarely are they seen on desks and tables and they are never found on walls.

Searches for this spider should concentrate on uninhabited areas close to the floor, particularly in boxes, around piles of paper, clothing, and debris, in closets, and under furniture. Periodic checks outdoors should focus on storage sheds, piles of debris or wood, cracks in the soil or in foundations, walls, and window wells, especially if small children play near these places. Employing traps in monitoring is also useful in establishing the extent of brown recluse infestations, and is helpful in providing a measure of control.

Management Options

Physical Controls

Because these spiders prefer undisturbed places for nesting and hiding, periodic, thorough cleaning can help reduce their numbers. Floors should be kept well-vacuumed. Boxes of paper and other items stored in closets, or anywhere else that is dark and undisturbed, should be handled carefully when first inspected. If brown recluse spiders are suspected, the boxes can be placed in a bin-type freezer for 48 hours to kill the spiders before the boxes are unpacked. A small hand-held, battery-powered vacuum can also be used while checking through stored items. If a spider is vacuumed up, the vacuum bag can be placed into a plastic bag and then into a freezer.

Outside, remove piles of debris, wood, and rock. Fill cracks in walls and foundations with mortar or caulk. Inside, clothing and other objects should be removed from floor areas in closets, locker rooms, and other storage spaces. Because most bites are received when putting on shoes or clothing that has lain on the floor, clothes normally stored near the floor should be moved to a higher location. Shake out clothes if they were on a floor overnight. Hanging shoes or placing them in sealed plastic bags reduces the likelihood of being bitten. Wearing leather gloves while searching through stored items can help prevent bites.

Aggressive House Spider

Identification and Biology

The aggressive house spider (Tegenaria agrestis) is a fairly large (1 3/4 inches, including legs), fast moving spider. Its legs are long and hairy and its body is brown with darker markings on its oval abdomen. This spider builds a funnel-shaped web in moist, dark places. The aggressive house spider waits in its funnel, and when it feels vibrations rushes out to grab its prey.

This spider mates in the summer and early fall, and the female lays eggs in the fall in silken sacs that are placed behind or beside the web. Eggs hatch in the spring and the spiderlings develop for a year before they are sexually mature.

The aggressive house spider is found throughout the Pacific Northwest, Idaho, and Utah and appears to be rapidly expanding its range.


Very few people are bitten by this spider and even fewer develop severe symptoms. Bites most commonly occur from July to September when males are wandering in search of females. Often bites occur when the spider is squeezed between clothing and a person's body. The bite of an aggressive house spider can produce symptoms similar to those produced by a brown recluse. The initial bite may not be painful, but within a few minutes a hard, sensitive area develops. Other symptoms include severe headache, nausea, weakness, and joint pain. Later, the area blisters, oozes serum, and eventually scabs over. The lesion may take months to heal.

Detection and Monitoring

The distinctive funnel-shaped web of the aggressive house spider is easy to spot in dark, moist locations at ground level or in basements. Specially designed traps may be useful in detection and possibly control.

Management Options

Physical Controls

As with other spiders, regular, thorough vacuuming behind furniture and stored articles, under baseboard heaters, and in closets will help eliminate spiders and their webs. Repair torn screens and broken windows, and ensure that doors are able to close tightly without gaps. If this spider is common in your area, do not store shoes, clothing, or bedding at ground level where spiders could become entrapped. Outside, caulk holes and crevices in foundations or walls and eliminate piles of debris, lumber, and rocks, as much as is possible. Cut or eliminate long grass growing near foundations. Wear protective clothing when working outside in areas that might harbor spiders and inspect items that you pick up. Always check articles that you bring into the school from outside storage sheds to make sure you don't bring in spiders or their egg sacs.

Edited by: Deanna Branscome, University of Florida.
Originally written by: S. Darr, T. Drlik, H. Olkowski, and W. Olkowski

Photographs and Graphics: University of Florida

Published: May, 1998