Spiders are survivors, constructed by nature to withstand adverse environmental conditions and long periods without food. Their significant reproductive capacity also contributes greatly to their abundance. The architecture of their bodies, their solitary nature and their ability to adapt make them a formidable adversary to control in and around structures. “Control” is the right term because total elimination of spiders in or on a building is nearly impossible except in select situations and only after significant expenditures of energy and resources.

So how does one approach controlling these arthropods — the arachnids? Depending on the spider and the situation, the strategy may not be an easy one. But for most homes and buildings, spiders can be kept to a minimum without a lot of fuss and work.

INVESTIGATE AND ANALYZE. Before any program to control or manage a particular pest can be devised and implemented, the situation has to be examined carefully. Each building and the spider population in and around it will be unique and will differ even from the building next door. As always, Situational Pest Management (SPM) must be practiced by taking into account 1) which types of spiders are present; 2) where they are active; 3) where spiders might enter; and 4) what factors may be contributing to the presence of spiders.

Tom Fortson of Terminix in Columbia, S.C., has developed a concept that fits in nicely with this author’s vision of SPM. He argues that we, in this industry, should not “inspect,” rather we should “investigate.” Inspection, after all, is defined as “to look over” or “to view.” Investigation refers to “observing or studying by close examination and systemic inquiry.” In simpler terms, to look deeper and gather clues by which informed opinions and conclusions can be formed.

The person conducting the initial survey of the structure affected by spider activity must look at the overall picture and ask why the spiders are present in the first place. The answer may not be obvious in every situation, but in others it might. For example, one office building in Florida was located near a containment pond used for storm water drainage. The numbers of spiders on the outside of the building were tremendous, supported by the large number of flying insects that were breeding in the pond and then traveling at night to the bright lights on the building. When the exterior fixtures were outfitted with sodium vapor lamps, the spider population crashed significantly because the available food supply dropped. That still left plenty of spiders, however, and acceptable control was not achieved until the pond was totally drained at a later date.

Items the investigator must look for include the types of spiders involved and where they are active, as well as the conditions contributing to spider activity. Such conditions should include those that support insects that serve as the spiders’ food source. Another factor to consider is how spiders are entering the structure.

Types of Spiders. Basically, three types of spiders, based on how they acquire food, will be encountered: hunting spiders, passive hunters, and web builders.

Hunting spiders actively forage for insects and will enter buildings as they search for prey. Much of the control efforts for such spiders will be directed at the exterior. Some situations, such as those involving wolf spiders, will require some interior treatments and the use of traps. Examples of hunting spiders include wolf spiders, ground spiders and jumping spiders.

Passive hunters, such as the brown recluse, sit in wait for prey to happen by. One to a few may first enter a building and then establish a breeding population. Brown recluse spiders often hide in voids and cracks both inside and outside the building, so inside and outside efforts are usually needed.

Web builders capture prey by constructing various types of webs. The structure of the web is often an excellent clue to the type of spider involved. Web-building spiders will be found inside and outside a building from the sublevels to the attic. These spiders are the bane of most homeowners, as the cobwebs they leave behind are unsightly and create a continual cleaning task. The presence of black widow or hobo spiders is a greater health concern and requires considerable efforts.

Contributing Conditions. Spiders are a product of the environment surrounding a building. Although buildings in a wooded area are more likely to experience larger infestations, any building can be subject to a significant spider problem. Spiderlings of web-building species disperse by “ballooning” which propels them through the air on strands of silk. High-rise buildings in downtown areas of major cities experience large numbers of spiders, even on the highest levels. Likewise, a building surrounded by huge parking lots can develop a bad spider problem. The spiderlings balloon to the building and the structure’s lights attract the flying insects they need for food. A good investigator looks at all the “angles” to determine the underlying causes of the spider problem.

Heavy vegetation is a particular factor in the numbers of hunting spiders. Because they are typically located at ground level, such spiders as the wolf spider find plenty of insects to catch in heavy ivy or other ground cover. Eliminating or minimizing such vegetation, especially next to the foundation, decreases spider activity. Similarly, items lying in contact with the soil provide cover for both insects and spiders. Leaf litter, lumber, stones and other items can harbor considerable numbers of hunting spiders. Piles of items provide structure to which web-building spiders can attach their webs. Brown recluse spiders prefer to harbor in such unstructured “clutter.” Removing it results in fewer spiders and insects.

Excessive moisture in crawlspaces also contributes to larger spider populations. The installation of foundation vents and other moisture control methods is therefore important to keeping a home relatively free of pests, including spiders. Proper attic ventilation is another area that deserves investigation. The brown recluse is especially common in attics from which it invades the living spaces below.

Exterior lighting attracts flying insects to a building. Changing this lighting to sodium vapor lamps on commercial buildings or yellow “bug” lights on homes greatly decreases the number of insects attracted. Fewer insects generally results in fewer spiders. Cracks and holes in the building’s exterior permit spiders to enter; therefore, exclusion efforts are very productive in managing spiders. In addition, all foundation and attic vents need to be equipped with screens, and doors need to have tight-fitting weatherstrips at the bottom.

SPIDER CONTROL OVERVIEW. The three factors of paramount importance in controlling spiders are sanitation, harborage removal and exclusion. The type of exterior lighting is also important. The more spiders due to contributing conditions, the more likely many spiders will manage to invade the building. Insecticide treatments can kill only so many spiders. Minimizing the total numbers of spiders around increases the effectiveness of other control efforts.

When controlling spider infestations, recommend that the customer remove or minimize heavy vegetation and remove any other potential harborages (e.g. leaf litter, piles of items, etc.). Also, as many cracks and holes as possible need to be sealed. The customer can complete this task, or the pest management professional can offer this as a service.

Remove spider webs and web-building spiders from the outside of the building on a regular basis. Many professionals include this step as a regular part of the pest control service. The Mighty Cobweb Duster sold by Sunshine Industries is an effective tool for this task, permitting the user to reach up to 15 feet or more. Permitting cobwebs to accumulate may give the appearance of a bad spider problem although few live spiders may actually be present. At the very least, regular web removal provides the appearance of spider control to the customer. Inside web removal is also beneficial. Although the professional can remove webs during his or her service, the homeowner should be advised to remove webs and spiders weekly to assist in the effort.

Controlling Hunting Spiders. Wolf spiders and ground spiders are the two most common types of hunting spiders invading buildings. Monitoring traps and spot treatments with residual insecticides are the key control methods used. Monitoring traps should be placed along baseboards in areas where spiders have been seen. Traps need to be located in protected sites, such as under furniture and behind items, where spiders are more likely to be found. Traps should also be located under items near entryways to capture spiders as they enter. In homes, permanent monitoring traps should be located in a garage on either side of the overhead door. The Kness Stick-All and the Bell Labs Pest Monitor are two examples of monitor stations that work well in garage environments.

Spot treatments using a microencapsulated or wettable powder formulation are often helpful when numerous hunting spiders are invading a home or other building. Such treatments should be applied along baseboards under and behind furniture and other items in areas of activity. The wall/floor juncture in the garage and in warehouses may also be treated, especially close to doorways.

In buildings where wolf spiders are regularly seen, treatment of exterior cracks and holes near the foundation using a residual dust should be completed. A perimeter treatment up to several feet out from the foundation may also be helpful. For large commercial buildings such as warehouses, regular perimeter treatments are often needed to minimize spiders inside. Still, these treatments are greatly reduced in effectiveness if harborage removal and exclusion efforts are not implemented.

Controlling Web-Building Spiders. Regular removal of spiders and their webs is an important step in controlling these types of spiders. Where hunting spiders are often difficult to find, web builders are easy to see due to their webbing. The difficulty in controlling these spiders lies not in eliminating the existing spider population inside but in preventing new spiders from invading. Existing webbing, live spiders and their egg sacs need to be removed. The most efficient way to accomplish all three is using a vacuum. In commercial situations, ladders or lifts may be needed to reach spiders.

Exterior lighting needs to be changed to a type that attracts fewer flying insects. Doors and windows need to be kept closed or be equipped with tight-fitting screens. Cracks need to be sealed around doors and windows, and doors need tight weather-stripping around the edges. Crawlspaces in attics need to be well ventilated.

Spot treatments using an ME or WP insecticide can be applied to corners indoors where spider activity has been noted. Such treatments should be applied following web removal. Outside, spot treatments should be applied to soffits and the corners of windows and doorways (following removal of webbing). Any other corner where spiders could attach webs should also be treated.

In review, identify the type of spiders involved, investigate the situation to determine the underlying causes, address the contributing conditions affecting the spider population, remove spiders and their webbing, and apply appropriate treatments. Follow these steps and spider control can be easy. It may just take a little effort.

Stoy A. Hedges is manager of technical services for Terminix International, based in Memphis, Tenn.