Structural and Public Health Pests: Spiders

Pest Management In and Around Structures March 23, 2010 Print Friendly and PDF

Spiders (Order Araneae) are often more of a perceived pest than a clinical risk. There are several species capable of inflicting a harmful bite, but relatively few envenomations result in long-term injury. Spiders generally will not bite unless accidentally trapped against the skin or grabbed. Some species actively guard their egg sacs or young. Many spider species are too weak to puncture human skin. When envenomation does occur, mild reactions may include slight swelling, inflammation, burning or itching sensations lasting a few hours. Spiders of medical significance include widow spiders (Latrodectus spp.), recluse spiders (Loxosceles spp.) and yellow sac spiders (Cheiracanthium spp.).

Spiders are often implicated by medical professionals when patients present skin lesions. However, a US study showed that of 600 cases of suspected spider bites, approximately 80% were not caused by spiders. Very few fatalities occur, usually fewer than three annually. Widow spiders have a neurotoxin in their venom, which is potentially lethal. In the United States approximately six percent of the reported bites prove to be potentially fatal (Meier, J, and J. White (1995) Handbook of Clinical Toxicology of Animal Venoms and Poisons. CRC Press, Boca Raton). Most often it is children under 18 kg (40 lbs), hypertensive individuals, or the elderly with immune deficiencies who are compromised, therefore, most sensitive. The majority of all widow bites (70%-80%) result in a local painful reaction. There are 11 native recluse species in the US. Additionally, two non-native species of recluse species are found in certain areas: Loxosceles rufescens (Mediterranean recluse), and Loxosceles laeta (Chilean recluse). Recluse bites initially produce a reddened area which may form a bulls-eye lesion and blister, and eventually may give rise to a necrotic wound (an open, weeping wound characterized by dead tissues and slow healing). If not tended to, this can lead to disfiguring scarring; however, recluse bites are rarely fatal. Sac spiders have been reported as responsible for more bites than any other spiders (Anonymous. Prescription Treatment University Online. www.pt-u.com/) The result of a yellow sac spider bite may be immediate pain followed by redness and a burning sensation at the site of the bite, perhaps with blistering and swelling. Rarely does an open sore develop. At the present time there is no scientific evidence to support the theory that Hobo spiders, Tegenaria agrestis, aggressive house spider, T. domestica, or the giant House spider, T. duellica. have necrotizing venom. Spider bites may cause immediate pain followed by redness and a burning sensation at the site of the bite, perhaps with blistering and swelling. Spiders are beneficial predators that reduce pest populations (flies, crickets, mites, etc.) in and around buildings. Wholesale destruction of spiders should be avoided. Table 8.50 Spider species most likely to be encountered in or around schools and other structures.

Common and species name Geographic distribution
Cobweb or Black Widow Spiders (Theridiidae), Latrodectus mactans, L. hesperus, L. geometricus, L. bishopi, L. variolus, Steatoda spp., Theridion spp. Throughout the US.
Orb Weaver Spiders (Araneidae), Argiope spp., Neoscona spp.,Tetragnatha spp. Throughout the US.
Funnel Web or Hobo Spiders (Agelenidae), Tegenaria agrestis, T. domestica, T. duellica, Agelenopsis. T. agrestis occurs from Idaho to Vancouver ad Winnipeg.
Cellar Spiders (Pholcidae), Psilochorus spp., Physocyclus spp. Throughout the US.
Wolf Spiders (Lycosidae), Schizocosa spp., Hogna spp., Rabidosa spp., Pardosa spp. Throughout the US.
Jumping Spiders (Salticidae), Menemerus bivittatus, Phidippus spp., Anasaitis canosa. Throughout the US.
Nursery Web Spiders (Pisauridae), Pisaurina spp. Throughout the US.
Crab Spiders (Thomisidae and Philodromidae), Misumenops spp., Xysticus spp., Tmarus angulatus, Coriarachne brunneipes, Tibellus sp. and Philodromus sp. Throughout the US.
Spitting spiders (Scytodidae), Scytodes spp. Throughout the US.
Woodlouse spider (Dysderidae), Dysdera crocata. Generally east of the Mississippi R.
Recluse spiders (Loxoscelidae), Loxosceles reclusa, L. deserta, L. arizonica. L. reclusa is found south to the Gulf of Mexico, north to Illinois, west to Oklahoma and east to Tennessee and Georgia; L. deserta in southeastern California and western Arizona; L. arizonica in south central Arizona.
Tarantula (Theraphosidae), Aphonopelma chalcodes, Eurypelma californicum. Texas, Oklahoma and west to southern California.
Sac spiders (Clubionidae), Cheiracanthium spp. Throughout the US.

Monitoring and inspection for spiders

Monitor for outdoor spiders at night with a flashlight or head lamp. This is the time when they are most visible. When making your inspections, focus on areas that are dark and undisturbed during the day, but not necessarily close to the ground. Check small cracks and crevices from the foundation to the eaves of buildings, under outdoor furniture, piles of wood, bricks, stones, around burrows, water meter and irrigation boxes, sheds, etc. Indoor spiders often become trapped on sticky traps.

Non-chemical management for spiders

General cleaning, reducing clutter, and harborage, can help reduce numbers. Vacuuming of webs, egg sacs and spiders is the most instant control method. Clothingand foot wear should be removed from floor areas in locker rooms, and other storage spaces. Many bites are sustained when putting on shoes or clothing that has lain on the floor. Outside, remove piles of debris, wood and rock. Fill cracks in walls and foundations with mortar or concrete sealant. Remove heavy vegetation and leaf litter around the foundation. Wash spider webs off the outside of buildings using a high-pressure hose. Good exclusion practices include:

  • Tight-fitting screens on windows and doors; also install weather stripping and door sweeps.
  • Seal cracks and crevices where spiders can enter buildings.
  • Equip vents in soffits, foundations, and roof gables with tight-fitting screens.
  • Install yellow or sodium vapor light bulbs outdoors; locate lights away from the house or turn them off when not needed.
  • Tape the edges of cardboard boxes to prevent spider entry.
  • Use plastic bags (sealed) to store loose items in storage areas.

Table 8.51 Commonly used products for physical, cultural or mechanical management of spiders and uses.

Type Example Products Uses
brush Quickie Telescoping Web Duster Brush on telescoping pole used to remove spiders, egg cases, webbing.
vacuum, HEPA filtered Sierra Backpack Vacuum Vacuum removal of spiders, egg cases, webbing.

Pesticide options for spider management

Vacuuming individual exposed spiders and egg sacs is far more effective than non-residual pesticides and many residual pesticides as well. Pesticide applications are unnecessary and often ineffective in reducing spider complaints. Existing egg sacs are often unaffected by aerosols. Residual liquid sprays applied to the outside perimeter of buildings are not very effective for species that display web-sitting behavior. Pesticide space treatments often fail to contact spiders in protected daylight harborages. Several species are affected minimally even if fully exposed. Barrier applications of residual-active pesticides to exposed impervious surfaces including foundations, walkways and driveways are prone to runoff into surface water and should be avoided.

Non-repellent dust formulations applied to webs are often more effective. Residual dusts can be applied to voids and inaccessible areas where spiders hide. Wettable powders or microencapsulated formulations of residual pesticides are sometimes applied to corners, in storage areas, etc. to control active hunting spiders and reduce reestablishment of new spiders. Aerosol flushing agents such as pyrethrins, though ineffective by themselves in providing long-term control, can cause spiders to move about so that they can be removed with a vacuum.

Table 8.52 Commonly used pesticides for spiders. a. Insecticides carrying a CAUTION label or exempt from EPA registration, in formulations that reduce potential for exposure.

Type Example Products Uses
undisclosed non-hazardous substances as defined by OSHA‘s hazard communication standard 29 CFR 1910.1200 Dr. T‘s Cobweb Eliminator Breaks down the spider web attachment points and makes for easy to remove. A residue remains that makes reformation of the web difficult. May be applied to wood, painted surfaces, vinyl, fiberglass, concrete, masonry or metal surfaces.
2-phenethyl propionate. EcoPCO ACU 67425-14 Aerosol.
2-phenethyl propionate, pyrethrins EcoPCO AR-X 67425-15 Aerosol.
eugenol (clove oil), 2-phenethyl propionate Bioganic Safety Brands™ Dust Insecticide EcoExempt D EcoExempt KO Contact dust formulations.
eugenol (clove oil), thyme oil EcoExempt™ G Granular insecticide.
thyme oil, 2-phenethyl propionate, pyrethrins EcoPCO WP-X 67425-25 Wettable powder.
mint oil, mineral oil (USP), lecithin Victor® Poison-Free® Ant & Roach Killer (EPA Exempt) Aerosol.
rosemary oil, oil of wintergreen, mineral oil EcoEXEMPT™ IC 2 (EPA Exempt) Concentrate, mix with an adjuvant.
garlic extract Garlic Barrier (EPA Exempt) Odorless concentrate. Not found to be effective.
diatomaceous earth DE is composed of finely milled fossilized shells of minuscule organisms called diatoms. The microscopically fine, sharp edges desiccate the insects' exoskeleton upon contact and the pests dehydrate and die within hours.

b. CAUTION-label formulations with greater potential for toxicity and/or exposure. Use less hazardous options.

Type Example Products Uses
amorphous silica gel, piperonyl butoxide, pyrethrin dust Drione Dust 73049-287 Sorptive dusts containing amorphous silica gel (silica aerogel) and pyrethrins, Particles of the dust affect the outer covering of spiders (and also insects) that have crawled over a treated surface, causing them to dry out. When applied as a dust-like film and left in place, a sorptive dust provides permanent protection against spiders. Dusts can be applied to cracks and crevices using a puffer.
acephate PT Orthene Crack & Crevice Pressurized Residual 499-373 Crack and crevice treatments.
bifenthrin Talstar One 279-3206 Labeled for inside, outside, and perimeter applications.
bioallethrin, sumithrin, coconut diethanolamide, naphtha, petroleum gases Ortho Flying Insect Killer 239-2512 Aerosol.
orthoboric acid Boric powder 9444-129 PIC Boric Acid 3095-2020 Apply to dry surfaces only. Lightly coat a thin layer of dust in the areas where pests are found or may hide such as cracks and crevices, behind and beneath stoves, refrigerators, sinks, cabinets, garbage cans, around pipes and drains, window frames in attics and basements.
cyfluthrin Tempo Ultra WP 432-1304 Synthetic pyrethroid, wettable powder.
cypermethrin Tempo Ultra SC 11556-124 Cy-Kick 499-304 Liquid formulation.
cypermethrin Demon WP 10182-71 Cynoff WP 279-3070 Synthetic pyrethroid wettable powder.
cypermethrin CB-Air Devil 9444-182 Synthetic pyrethroid low odor aerosol.
cypermethrin Demon EC 100-1004 Cynoff EC 279-3081 Synthetic pyrethroid odorless liquid emulsifiable concentrate which leaves no visible residue.
deltamethrin Suspend SC 432-763 Synthetic pyrethroid space treatment.
deltamethrin Delta Dust 4-441 Waterproof dust.
esfenvalerate Ortho Bug-B-Gon 239-2680 Concentrate.
imiprothrin, deltamethrin Raid Max Roach Killer 4822-518 Aerosol.
lambda-cyhalothrin Demand CS 100-1066 Spectracide Bug Stop 9688-176-8845 Water-based concentrate. Outdoor perimeter applications and barrier treatments as well as applications to lawns, turfgrass, and ornamentals. Indoors, can be used for crack and crevice treatments.
pyrethrins, piperonyl butoxide Revenge Farm & Home Fly Bomb 9086-8 565 PLUS XLO 499-290 Pyrethrin Aerosol, not effective used as a lone management tactic. Used as a crack and crevice application to flush or kill.
pyrethrum, piperonyl butoxide Kicker 432-1145 Flushing agent.
pyrethrins, permethrin Ortho Indoor Insect Fogger 239-2626 Fogger.
permethrin Dragnet SFR 279-3062 Indoor/outdoor spray.
pyrethrin, piperonyl butoxide, N-octyl bicycloheptene dicarboximide ULD BP-300 499-450 565 Plus XLO 499-290 Indoor or Outdoor Application as a space, area or contact spray.
prallethrin ULD Spy-300 1021-1718 Contact insecticide.
prallethrin, esfenvalerate, MGK-264 synergist Ortho Roach, Ant and Spider Killer 239-2679 Aerosol.
silica dioxide (from diatomaceous Earth), piperonyl butoxide, pyrethrins Perma-Guard 67197-6 Apply as a suspension or as a dust to cracks and crevices.

Emerging issues, new strategies and priorities for spiders

Expanding ranges of native species including the brown recluse and ongoing introductions of exotic species pose an increasing challenge for spider management. Education of physicians and other health professionals to promote accurate identification of suspected spider bites is also a challenge. Table 8.53 Priorities for spiders.

Research Efficacy of botanical pesticide products on spiders. Characterization of Tegenaria spp. venom. Safer antivenin treatments.
Education Improved knowledge base of medical professionals diagnosing spider bites. Support materials for schools contracting reduced-risk spider management protocols. Improved knowledge base of PMPs managing spiders.
Management Effective reduced-risk options information is lacking.

Additional resources for spider management

Arizona Cooperative Extension. 2004. Spiders. Pest Press. cals.arizona.edu/urbanipm/pest_press/2004/june.pdf (PDF) 123

Arizona Cooperative Extension. 2006. Recluse Spider. Pest Press. cals.arizona.edu/urbanipm/pest_press/2006/november.pdf (PDF) Bradley, R. 2002. Spider Bites. www.marion.ohio-state.edu/SpiderWeb/Spider%20Bites.htm

Edwards, G.B. 2002. Venomous Spiders in Florida. www.doacs.state.fl.us/pi/enpp/ento/venomousspiders.html Hedges, S.A., and M.S. Lacey. 1995. Field Guide for the

Management of Urban Spiders. 220 pp. Franzak & Foster Co., Cleveland, OH. University of California. 2008. Brown recluse and other spiders. In How to Manage Pests of Homes, Structures, People, and Pets. www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7468.html

University of California. 2007. Spiders. In How to Manage Pests of Homes, Structures, People, and Pets. www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7442.html

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