The Brown Recluse Spider and Other
Spiders Associated with Buildings

Although fear of spiders is common, dangerous types are not likely to be encountered in many buildings. However, the brown recluse spider, which can inflict a serious bite, has been found in buildings. Harmless, crawling spiders are occasionally a nuisance in basements or other areas. Tighter sealing around windows and utility access holes and tight weather stripping on exterior doors will usually reduce their numbers. Residual insecticide sprayed on surfaces near potential entry may help somewhat; dust and micro encapsulated formulations may have a greater chance for success. Spiders that build webs in secluded corners or in outdoor locations such as eaves or lights can be most efficiently controlled with a vacuum. The general approach of sealing up entry points and vacuuming up intruders should be the first consideration for most types of spiders (and other miscellaneous crawling pests, such as crickets and millipedes).

Wandering Spiders

Some spiders will enter buildings in search of food and shelter, particularly in the fall when the temperatures become cooler. Below is a list of spiders that are often found in or around buildings. Although many spiders can bite, the injury from this group is usually similar to a bee sting.

Cellar Spiders

Cellar spiders have long, thin legs and build sheet-like or irregular webs in dark places. They commonly hang upside down under the web.

Crab Spider

Small crab spiders are dark or tan; some are lightly colored orange, yellow or creamy white. Their legs extend out from their sides causing them to scuttle back and forth in a crab-like fashion. These spiders hide in flower blossoms and may be brought inside in cut flowers.

Jumping Spider

Jumping spiders are active during the day and are common around windows where they feed on insects attracted to natural light. Jumping spiders are usually small, up to ½ inch in length, and many are brightly colored. They move in quick rushes, jerks or jumps. They often enter buildings from shrubs near windows or ride in on plant blossoms.

Orb Weavers

Orb weavers include "garden spiders" and their relatives. They build sheet-like orb webs that consist of rays and spirals of silk. They have poor eyesight and have trouble walking on anything but webs. They rarely occur indoors but frequently live on or near the outer walls of buildings near lights. A common orb weaver is the large black and yellow garden spider.

Wolf Spider

The hairy, fleet wolf spiders are very common outdoors under leaf litter, rocks and logs. When they come inside, they normally stay on the ground floor and are active in dim light. Large, quick-moving wolf spiders often frighten people. If handled, they give a painful bite, but it is not usually dangerous.

Other Spiders

There are many species of spiders in Illinois. Images of some of the common spiders found in the Midwest may be found on the following Web sites: University of Nebraska -- < http://lancaster.unl.edu/enviro/pest/SpiderPhoto.htm > Missouri Department of Conservation – < http://www.conservation.state.mo.us/nathis/arthopo/mospider/kinds.htm >

Control and Management

If wandering spiders are found, the best approach is to limit their access to the buildings.

• Tighten door thresholds and around window screens.
• Caulk door and window frames and all wall penetrations.
• Remove vegetation and litter from the foundation, doorways and window wells.
• Where possible, relocate building or area lights that attract flying insects, especially midges.
• Carefully check flowers brought in from the garden and from commercial greenhouses.
• Indoors, eliminate old cardboard boxes and other clutter that provide hiding places for spiders.
• One can kill spiders with a fly swatter or vacuum spiders to kill them. When you are done vacuuming up spiders and their webs, seal the vacuum bag and place it in an outdoor trash container.
• Effective pesticide application for spider control is very difficult; indoor treatment is usually effective only if the pesticide contacts the spider directly. This means the pesticide application must be very thorough. Consequently, this may be a job for a licensed structural pest control company. Unless efforts are made to exclude spiders (such as tightening gaps around entrances and inspecting where materials like cardboard boxes are being brought into the building), spiders will reenter the building.

Brown Recluse Spider

The brown recluse spider is uniformly tan to brown without markings except for a dark fiddle-shaped mark. (Several other species of spiders may have similar markings.) Although they can be found living outdoors in southern Illinois, they can be introduced into buildings in other areas of the state where they have been transported in boxes, pallets or other items. The brown recluse makes a fine, irregular web. In indoor infestations, it commonly wanders in the evening while seeking insects as food.

Identification - Many common spiders are often confused with the brown recluse spider. If you want information about identification of a spider, please call the Department at 217-782-5830 or E-mail mailus@idph.state.il.us.

Bites - Brown recluse spiders avoid busy parts of rooms where people are present, remaining where there is no activity and in closed or unused rooms. Even though indoor infestations can be large, people are seldom bitten. Bites may occur when rooms are suddenly put into use or when stored clothing is brought out for use. Brown recluse bites are sharp but not initially painful, but a blister is quickly raised, broken and surrounded by a red welt. The depressed center of this raised, red circle (the size of a dime to a quarter) turns dark within a day. The dead tissue often falls away and the bite area scars over in one to eight weeks. Death seldom occurs, but the bite can result in a large and disfiguring scar. Individuals who believe they have been bitten by the brown recluse spider should immediately contact a doctor. If possible, the individual should keep the offending spider so it can be identified.

The spider is delicate. After biting, it frequently can be found lying where it was slapped by the victim. It should be killed and taken to the physician along with the victim for positive identification. Other biting or stinging insects (and related creatures) can produce injuries resembling the bite of the brown recluse spider. Furthermore, some cases of "brown recluse spider bites" are actually injuries from other causes such as bacterial skin infections. Before any pesticide application occurs, a thorough inspection for the brown recluse spider should be conducted.

Control and Management

Inspection

• Sticky traps are very useful in determining if brown recluse spiders are present. Place the sticky traps in corners or under furniture.
• Look along walls in uninhabited rooms, under and behind furniture, in the far reaches of storerooms, in unused closets, under stairs and in hanging clothes that have not been used during the current season.
• Concentrate on areas outside daily human traffic patterns. Buildings that have been unoccupied for months or longer are particularly susceptible to increased spider populations.
• Outdoors, in southern Illinois, these spiders may be found in cracks between the soil and structure foundations, in door stoops and in window wells.
• Habitat and Harborage Reduction

Carefully mop or dust seldom-used rooms and closets.

• Inspect clothing (such as that used in plays) that has hung in hallways or unused closets through the summer.
• When not in regular use, store these items in plastic bags.
• In the evening, re inspect spaces disturbed by dusting and mopping. Kill moving spiders.
  

Pesticide Application

• Carefully use residual pesticides labeled for spiders. Dusts and micro encapsulated insecticides are usually more effective than other formulations.
• Apply the pesticide in all cracks and crevices -- particularly in spaces outside daily human traffic patterns. Spot treatments will be less effective than crack and crevice treatments because spiders touch spot residues only with hairs at the tips of their legs.
• When a population of the brown recluse spider is established in a building, effective control can take months of monitoring. Consequently, when the brown recluse spider has been positively identified in a building, the owners should consider hiring a licensed structural pest control company. Information about hiring a structural pest control company may be found at http://www.idph.state.il.us/envhealth/pcpestcntrl.htm.
  

Follow-up

Spiders not killed by the pesticide treatment will wander. Consequently, be wary when picking up items in rooms not normally in use and watch carefully for spiders for one or two days following treatment. Monitor and, if indicated, retreat the structure in one or two weeks. Infestations of the brown recluse spider may be difficult to eliminate completely; continue to monitor infested areas with sticky traps for several months.

CAMEL SPIDER PICTURES

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