The majority of spiders found inside and outside the home are not harmful to humans, will avoid human contact as much as possible and actually serve a beneficial purpose in natural ecosystems by preying on problematic insects like flies and mosquitoes. Human death is rare, even among much-feared species like the black widow and brown recluse.
Still, homeowners may wish to remove spider infestations from their homes altogether. To a substantial extent, the choice of which insecticide is most effective depends on the severity of the spider infestation.
Probably the most common means of controlling spiders is by spraying them with a contact insecticide. Carbaryl, bendiocarb, chlorpyrifos or synthetic pyrethroids such as Cypermethrin, Cyfluthrin and Lambda-cyhalothrin are all active chemical ingredients of contact insecticides.
Any spray insecticide that is rated for spider control, however, will be effective when sprayed on spiders or webs. Note that contact insecticides rarely affect spider egg sacs.
Total Release Foggers
Serious spider infestations should be treated with total release aerosol foggers, commonly referred to as "bombs" Aerosol foggers typically include synergized pyrethrin or synergized pyrethroids such as Resmethrin, Sumithrin and Cyfluthrin as their active insecticidal ingredients. "Bombing" the entire house can be much more efficient than spraying contact insecticides on observed spiders and can be effective at killing hidden spiders.
Critical spider infestations must be treated by a professional exterminator. Exterminators are licensed to carry and apply insecticides that consumers cannot legally purchase due to their high toxicity.
The higher toxicity, or course, also makes them more lethal against spiders. Professional exterminator treatments for spiders can be costly and disruptive to home life, so before contacting an exterminator, make sure the spider infestation is serious enough that you cannot control it on your own with store-bought insecticides.
Non-Chemical Control Methods
Choose from a nearly limitless list of non-chemical methods to treat spiders. These methods are not only less potentially toxic to humans but can often be sufficiently effective against infestation.
Spiders only linger in areas with sufficient food, so taking any measures to control populations of mosquitoes, flies, wasps and any other arthropods will also aid in reducing spider infestations.