Most common spiders in North America are not dangerous and are, in fact, beneficial insects, feeding on other insects that are generally considered to be pests of humans. However, this does not mean that we are adapted to living with spiders in our homes. In fact, while most spiders that are common to North America are shyer than they are aggressive—avoiding humans unless attacked or handled—many people fear spiders and their storied bite.
Differences Between Spiders and Insects
Spiders are easily distinguished from other insects by three physical characteristics:
- Spiders have eight legs, whereas insects have six.
- Spiders have two body segments, whereas insects commonly have three.
- Spiders may have six to eight eyes; insects usually have two.
The most effective means of controlling spiders is through implementing Integrated Pest Management (IPM) methods. This involves a strategic combination of exclusion, sanitation and chemical and non-chemical controls:
- Exclusion. Preventing entry of spiders is one of the first methods of control. Caulk or otherwise seal cracks and crevices in the home's structure through which spiders can enter. Inspect and repair screening on all doors and windows to ensure there are no holes or tears and that they are tightly fitted in their frames. Check for gaps beneath and around doors and windows, and seal these as well. (This is also beneficial for winterizing your home for energy savings as well as reducing general pest intrusion.)
- Sanitation. Spiders (and other pests) will take shelter and make their homes in piles and items that are rarely moved. This is one reason that people are prone to encounter spiders (and other pests) when moving or searching through rarely touched stored items in the basement or attic. To reduce or eliminate these forms of shelter, clear out any debris, trash, paper piles, and other unsanitary or seldom-used items. Regular sweeping and dusting will also keep areas clear and remove current or old cobwebs. This not only reduces the sites for spiders to harbor and breed but also reduces or eliminates insect prey they rely on for food.
- Non-chemical controls. Often, spiders are found individually or with newly laid eggs. When this is the case, the simplest method of control often is manual removal. You can pick up the spider and its web and eggs and discard them; wear gloves or use a tissue or cloth. You can also suck them up with a vacuum. Place insect sticky traps (sold at home centers and hardware stores) in corners and along baseboards to capture moving spiders.
- Chemical controls. For chemical control, apply residual insecticide to corners and other sites where spiders spin their webs and lay their eggs. Recommended products include those that contain pyrethroids (bifenthrin, cyfluthrin, permethrin, tetramethrin) and are labeled for such applications. This type of treatment tends to be more effective on spiders (and less toxic for the home environment) than the use of total-release foggers containing pyrethrins.
- Outdoors. In most cases, there is little need to control spiders outdoors. However, when they appear in large numbers on buildings, they can be washed off with a strong spray of water. Additionally, prevention techniques can help keep spiders from being attracted to your home (and eventually making their way inside). These include general insect prevention techniques, such as replacing standard mercury vapor lights with high-pressure sodium vapor or halogen lights. Although it is common to place lights on exterior walls near doors, it is better to place lights farther away, using pole lights when possible, with the light shining toward the door for safety.
Anything that reduces the attraction of a number of other insects in or around your home will help to reduce spiders as well. This is because the insects themselves—as a food source—are a primary attractant to spiders.