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Spiders

Getting to Know Spiders

Many people find spiders repulsive and scary, yet the majority of spiders are harmless and beneficial.1 So let's take a good look at these creatures and address our fears. Consider how much bigger you are than a spider 2 and that spiders probably can't even see you. Although spiders typically have eight eyes, many have poor eyesight.3 Spiders pose no real threat to us. In fact, you can appreciate spiders for their significant contribution to insect control.1

Identifying Spiders

Spiders differ from insects in a variety of ways. Spiders have eight legs, whereas insects have six. Insects have three body sections and spiders just have two. These two parts are the cephalothorax, which contains the eyes, mouth and legs, and the abdomen, which includes most everything else. Spiders do not have wings or antennae.4

Almost all spiders spin silk.3 Some spin beautiful round webs, and others use the silk to make funnels, sheets, or tangles.5 Some young spiders travel long distances sailing on threads of silk.6

The Good Side of Spiders

Spiders play an important role in controlling insect populations. An arachnologist (a person who studies spiders) in the United Kingdom once calculated that the weight of insects eaten by spiders in that country every year exceeded the weight of the people who live in the U.K.7

Some gardeners encourage spiders to live in their gardens to kill unwanted pests. Using mulches helps spiders by giving them habitat with a moderate microclimate. Planting caraway, dill, fennel, cosmos, marigold, or spearmint also encourages spiders.8

Potential Threat?

Most spiders are not poisonous to human beings. There are about 3,000 different spiders in North America, but only a few of them cause problems for people.2

If you are bitten, try to capture the spider that bit you if you can catch it quickly and safely. Later, if needed, you can get an accurate identification of the spider.9

The Problem Spiders

Only four kinds of spiders are known to cause health problems in the U.S.

Tarantulas

Tarantulas are large, hairy spiders found in the southern United States. Scary to some because of their large size, these spiders are not as dangerous as is commonly thought. Their bite causes little lasting pain or serious problems. However, their hairs can can cause an allergic response.2

Black Widows

The black widow female, but not the male, is big enough to bite a person. She is about 1/2 an inch long and shiny black.1 She is easily recognized by the red hourglass design on the bottom of her abdomen.10 Black widows are found throughout the Northwest.1,2,10,11 They tend to live in dark, dry, undisturbed places including garages, barns, sheds, wood piles, and outhouses.1 Most bites occur when cleaning out or picking up objects in these kinds of places. If you are bitten, the pain spreads from the bite to other places. Sometimes spasms occur. Children, elderly people, and people with other problems are likely to have more severe symptoms.1 If you are bitten you should get medical attention.10

Brown Recluse Spiders

Brown recluse spiders come in various shades of brown. They have black violin- shaped markings on the back of the cephalothorax, although sometimes this can be hard to see. They have six eyes (most spiders have eight) and fine hairs on their legs and abdomen.12 Brown recluse spiders are common in the central Midwest and South. They do not occur in the Pacific Northwest except when they hitchike from elsewhere. 2 California deserts have some native relatives of the brown recluse, and a South American relative has become established in the Los Angeles area. 12 Brown recluse spiders are shy (as their name implies) and active at night. They are often found under trash cans, tarps, and in similar locations.12 Their bite causes stinging, followed by intense pain. A blister forms at the bite and the area becomes swollen; later the tissue dies, leaving an ugly scar.10

Hobo Spiders (Aggressive House Spiders)

The hobo spider is common in the Pacific Northwest. It has long legs and chevrons on its abdomen.11 It is common in basements and window wells, and is usually found on the ground floor of a house. It is called "aggressive" because it bites willingly if it is cornered.10 Bites from this spider are relatively rare, but do cause open, localized wounds that can take a long time to heal.

Preventing Spider Problems

There are many ways to make your home less appealing to spiders. If there are cracks in your foundation or around windows and doors, seal them up.13 Check places where water pipes and electrical lines enter your house, and caulk any openings.2 Keep woodpiles and debris away from your house.10 In storage areas, put boxes up off the floor and away from walls. Seal boxes with tape to keep spiders from living inside them. In general, cleaning up clutter will mean you have fewer spiders.1

Pruning vegetation away from your house and keeping the area next to the foundation clear will also make your house less attractive to spiders.1 Outdoor lighting sometimes attracts insects, which in turn attracts spiders. You can move outdoor lighting away from windows and doors if this is a problem around your home.1

Removing Spiders

You can remove a spider from inside your house by putting a jar over it. Then slip a piece of paper under the jar so that the opening is sealed, pick up the jar, and take the spider outside.1

A good vacuum cleaner easily removes spiders and their webs from your house.2 Since spiders have soft bodies, they usually don't survive vacuuming.1 A broom is also a useful tool for moving a spider outside.10

Crushing spiders with a fly swatter,13 rolled up newspaper, or your shoe 1 are other simple ways to deal with unwanted spiders.

Chemicals Are Ineffective

Using a pesticide is not a good solution to spider problems. "Insecticides will not provide long-term control" of spiders, according to the University of California, "and should not generally be used against spiders outdoors." Inside, "control by spraying is only temporary unless accompanied by housekeeping."1 Washington State University Extension has a similar perspective: "Most spider problems can be solved without the use of chemicals."2

Summary

Remember that spiders are beneficial overall, and we should make an effort to appreciate them more and fear them less. "Spiders are far more beneficial than they are dangerous. The benefits we realize from spiders preying on insects, mites, and other spiders far outweigh the low potential health hazard to humans."2

Chemical spraying may well be be more dangerous and less effective than you think, so use simple pesticide-free techniques and be creative in controlling spider habitat.

References

  1. University of California. Division of Agriculture and Natural Resources. 2000. Spiders. Pest notes. http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7442.html
  2. Washington State University Extension. Undated. Spiders. EB 1548. http://cru.cahe.wsu.edu/CEPublications/eb1548/eb1548.html
  3. O'Toole, C. ed. 2002. Firefly encyclopedia of insects and spiders. Buffalo NY: Firefly Books, Ltd. p. 201.
  4. Ref. # 3, pp. 196-197.
  5. Ref. # 3, p. 209.
  6. Ref. # 3, p. 206.
  7. Ref. # 3, p. 205.
  8. Appropriate Technology Transfer for Rural Areas. 2000. Farmscaping to enhance biological control. http://www.attra.org/attra-pub/farmscape.html
  9. U.S. National Library of Medicine and the National Institutes of Health. 2005. MedlinePlus medical encyclopedia: Insect bites and stings. http://www.nlm.nih.gov/medlineplus/ency/article/000033.htm
  10. Montana State University Extension Service. 2005. Spider identification and management. MT 199210. http://msuextension.org/publications/AgandNaturalResources/MT199210AG.pdf
  11. Oregon State University. 2005. Poisonous spiders, ticks and other biting mites in Oregon. http://www.ent.orst.edu/urban/spiders.html
  12. University of California. Division of Agriculture and Natural Resources. Brown recluse and other recluse spiders. Pest notes. 2000. http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7468.html
  13. Finnigan, BF (University of Idaho. College of Agriculture.) Undated. Just the facts - sheet. Insect and pest information. Topic: Hobo spider.
    NOTE: The Finnigan article is no longer available online. A different fact sheet on hobo spiders is available at: University of California. Division of Agriculture and Natural Resources. 2006. Hobo Spider. http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7488.html

Originally published: "Getting to Know Spiders" by Pete Haws in 1995. Journal of Pesticides Reform 15(4):22-23
Updated September 2005 by Caroline Cox.
Links updated October 2010

Photos courtesy of Jim Kalisch, University of Nebraska-Lincoln Entomology Department, and the Centers for Disease Control and Prevention.