Spiders

Although fear of spiders is common, poisonous types are not likely to be encountered in most public or commercial buildings. However, the brown recluse spider has been found in schools, particularly in the southern part of Illinois. Harmless, crawling spiders are occasionally a nuisance in basements or other areas. Tighter sealing around windows and utility access holes and tight weatherstripping on exterior doors will usually reduce their numbers. Residual insecticide sprayed on surfaces near potential entry may help somewhat; dust and microencapsulated 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
Spiders will enter buildings in search of food and shelter. Below is a list of spiders that are often found in or around buildings. Although most spiders can bite, the injury from this group is similar to a bee sting.

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 wolf spiders often frighten people. If handled, they give a painful bite, but it is not dangerous.

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 1/2 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.

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.

  • Control and Management

    If called on to eliminate wandering spiders, the best action is to locate specimens, identify them, assure staff that they are not poisonous and tell staff how they got inside.

    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.
    Advise staff to look carefully at flowers brought in from the garden and from commercial greenhouses.
    Assure staff that they can swat or vacuum spiders without harm.

    Pesticide application is very difficult; indoor treatment is usually effective only if the pesticide contacts the spider directly. This means the technician must have access to all spider habitats. Unless efforts are made to exclude spiders (such as tightening gaps around entrances and inspecting where materials are being brought into the facility), spiders will reenter.

    Brown Recluse Spider
    The brown recluse spider is uniformly tan to brown without markings except for a dark fiddle-shaped mark. 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. It commonly wanders in the evening in indoor infestations.

    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.

    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. Consequently, some cases of "brown recluse spider bites" are actually injuries from other causes. 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.
    • 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, door stoops and in window wells.

    Habitat and Harborage Reduction

    • Recommend careful mopping or dusting of seldom-used rooms and closets.
    • Inspect clothing (such as that used in plays) that has hung in hallways or unused closets through the summer. Store them in plastic bags.
    • In the evening, reinspect spaces disturbed by dusting and mopping. Kill moving spiders.

    Pesticide Application

    • Carefully use residual pesticides labeled for spiders. Dusts and microencapsulated 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.

    Follow up
    Spiders not killed by the pesticide treatment will wander. Warn staff to be wary when picking up items in rooms not normally in use. They should watch carefully for spiders 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.

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    • Illinois Pest Control Association - 600 S. Second St., Suite 403, Springfield, Illinois 62704
    phone 217.544.7109 fax 217.528.6545
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