N,N-Diethyl-meta-toluamide, commonly known as DEET, is the most widely used active ingredient in insect repellents globally. Developed in the 1940s, it is applied to the skin or clothing to prevent bites from disease-carrying pests. DEET is primarily recognized for its effectiveness against flying, blood-feeding organisms such as mosquitoes, ticks, and biting flies. However, there is often confusion regarding its protective capabilities against all types of household pests.
Is DEET Effective Against Spiders
DEET is not considered an effective or recommended solution for repelling spiders. This lack of efficacy stems from fundamental biological differences between spiders and the insects DEET targets. Spiders belong to the class Arachnida, while pests like mosquitoes and flies are from the class Insecta. Although ticks are also arachnids and are repelled by DEET, they are blood-feeding parasites, engaging the chemical differently than predatory spiders.
The primary function of DEET is to interfere with the sensory organs of insects seeking a blood meal. Spiders are predators that hunt other arthropods and do not seek human hosts for feeding. Consequently, the mechanisms successful against biting insects do not translate into a reliable repellent for spiders. DEET is neither registered nor recommended as a primary chemical for spider control.
The Science Behind DEET Repulsion
DEET’s effectiveness against insects lies in confusing their olfactory system, making the host “invisible.” Flying insects, such as mosquitoes, locate humans by sensing volatile chemical cues like carbon dioxide and lactic acid. The DEET compound inhibits specialized odorant receptors on the insect’s antennae, preventing the detection of these host-attractant odors. This mechanism interferes with distance-based olfaction, which guides the pest to its target.
This mechanism fails with spiders because their primary sensory modalities for hunting and threat detection differ from those of insects. Spiders rely heavily on mechanoreception, sensing vibrations through specialized hairs on their legs to detect prey and movement. They also use contact chemoreception, a form of taste or touch sensation via their legs and pedipalps, rather than distance-based smell. Since DEET is designed to block airborne odor detection, it does not disrupt the spider’s vibration-sensing or contact-based hunting strategy.
Proven Methods for Spider Control
Because DEET is ineffective, controlling spiders requires methods that address their physical presence and reliance on a prey source. Exclusion methods are an effective first step in reducing spider presence in any structure. This involves sealing small cracks and crevices around windows, doors, and foundation gaps that spiders use as entry points.
Reducing clutter, both indoors and outdoors, removes the dark, undisturbed hiding spots where spiders prefer to rest and reproduce. This includes cleaning up piles of debris, wood, or stones near the home’s exterior and removing stored items in basements and garages. Spiders are also attracted to areas with an abundant food source, so reducing outdoor lighting that attracts flying insects will indirectly reduce the number of spiders nearby.
Chemical Control
For chemical control, products containing pyrethroids are the recommended insecticide class for arachnids. These chemicals act as neurotoxins upon contact and are often applied as residual sprays to create a barrier around the home’s perimeter.
Natural Deterrents
Natural deterrents can also be used, though they often have anecdotal success. These include spraying a mixture of water and peppermint oil near entry points, as spiders dislike strong scents. Diatomaceous earth, a fine powder, can also be sprinkled in undisturbed areas, working by physically damaging the spider’s outer shell upon contact, leading to dehydration.