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What Chemicals Kill Brown Recluse Spiders?

Also called the violin spider, the brown recluse spider (Loxosceles reclusa) is a member of the family Sicariidae, which includes more than 100 species of venomous spiders. Although the brown recluse spider is not aggressive toward humans, it bites when feeling threatened, causing a necrotic lesion on the skin. Insecticide sprays and dust contain chemicals such as deltamethrin, cypermethrin, bifenthrin, lambda cyhalothrin and cyfluthrin, which can kill the brown recluse spider.


Deltamethrin is the main chemical component of many dust insecticides, which effectively kill spiders, including the recluse brown. Although low in toxicity to mammals and birds, deltamethrin is toxic to bees, fish and other aquatic life, and illegal to use or sell in some states, such as New York, Connecticut, Rhode Island and Alaska.


Cypermethrin is a chemical compound present in many pesticides used in cotton fields and other crops, as well as in home pest control. Cypermethrin is moderately to slightly toxic to humans, according to concentration and formulation. However, it is highly toxic to aquatic invertebrates, fish and insects, including bees. It is also toxic to spiders, acting as a neurotoxin in their bodies and causing death. Cypermethrin use is banned in some countries, such as the United Kingdom.


An eye and skin irritant in humans, cyfluthrin is toxic to marine life, even in small concentrations. It can kill insects, spiders and other invertebrates by paralysis of their nervous system. This insecticide is often found in the form of aerosol, granules or concentrate liquid. Just as with other pyrethroid chemicals, such as cypermethrin and deltamethrin, the use of cyfluthrin is restricted in some states.

Bifenthrin and Lambda Cyhalothrin

Bifenthrin is insoluble in water and has a half life of up to four months in the soil. As with most insecticides, it kills small invertebrates by acting on their nervous system. The use of bifenthrin is prohibited in countries of the European Union due to its high toxicity to aquatic life and beneficial insects. Lambda cyhalothrin also acts as a neurotoxin in the brown recluse spider. The chemical accumulates in the tissues of fish and other aquatic life as well.

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