Most common spiders of the U.S. 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 the U.S. are shyer than they are aggressive – avoiding humans unless attacked or handled, many people fear spiders and their storied bite.
What Are the Differences between Spiders and Insects?
Spiders are easily distinguished from other insects, in that:
- 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.
How to Control Spiders
The most effective means of controlling spiders is implementing Integrated Pest Management (IPM) methods. That is a strategic combination of exclusion, sanitation, exclusion, non-chemical, and 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 the frame. 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 touch stored items in the basement or attic. To reduce or eliminate such harborage spots, clear out any debris, trash, paper piles, and other unsanitary or non-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 their available food – other insects.
- Non-chemical. Often, spiders are found individually or with newly laid eggs. When this is the case, the simplest method of control is often that of manual removal. The spider and its web and eggs can be picked up and discarded using a gloved hand – or in a tissue or cloth. A vacuum may also be used. Insect sticky traps, available at most home or hardware retail stores, can be placed in corners and along baseboards to capture moving spiders.
- Chemical. For chemical control, Colorado State University recommends the use of residual insecticides to corners and other sites where spiders spin their webs and lay their eggs, particularly those products that contain pyrethroids (bifenthrin, cyfluthrin, permethrin, tetramethrin) and are labeled for such applications. The experts recommend against the use of total release foggers containing pyrethrins, as these, they state, probably will have little effect on spiders.
- Outdoors. In most cases, there is little need to control spiders outdoors, however, when they occur in large numbers on buildings, they can be washed off "with a forceful jet of water." Additionally, prevention techniques can help keep spiders from being attracted to your home (and potentially, eventually, making their way inside). Such techniques include general insect prevention techniques, including, the replacement of 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 the light 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 it is, at lease in part, the insects themselves that attract spiders to an area – as food.
Control information adapted in part from Colorado State University.