Spiders

Spiders often are seen as ugly, threatening creatures. These eight legged, non-insect arthropods elicit fear and revulsion. Yet, they are a part of our every day world. They are viewed as beneficial when they capture insects but seen as pests when found inside the house.

Most buildings have a resident spider population feeding on household insects, stray flies, and each other. They live in neglected areas: attics, basements, behind and under furniture; bookcases or appliances; and in cracks between boards. Corners and baseboards are favorite locations.

Most house spiders are seldom seen except during housecleaning, but some of the larger species mature and become more active from late August to early October. At that time, the house may appear to have been invaded. Outdoor spiders do sometimes blow or crawl in through open windows, etc., but most either die of thirst in the house or fall prey to resident species.

Depending on your outlook, spiders in the house can be an advantage or disadvantage. A few spiders are rarely noticeable and help control other insects that find their way into the house. Spiders do, however, produce sheets or strands (cobwebs) of silk webbing, and small white specks of excrement which may drop on underlying items. People with allergies to spider venom, a fear of insects, or severe health problems should minimize the chance of any encounter with spiders.

It is surprising how people have developed a fear of spiders. People who really aren't afraid may automatically behave as if they were. Horror movies, other people and just plain misinformation about spiders often are causes for this fear. Teasing by parents or children creates false impressions and fear. Another factor contributing to the fear is spiders move quickly, giving the impression they are "after" us. Other spiders hang around at eye level, where we blunder into their webs. People consider spiders to be ugly and frightening. In truth many are quite handsome or graceful, and all of them are fascinating.

Whatever the cause for fear of spiders, the fear is real. With some thought, effort and accurate knowledge about spiders, it may be possible to reduce the fear of spiders.

Spiders are predators of insects and other creatures. Usually they only capture prey smaller than or equal to their own size. Humans are far too big, even for the most ambitious spider. Many spiders are small and have small mouth parts. These spiders are not capable of biting through human skin.

Spiders which can bite through human skin only do so when provoked. Often bites occur when the spider is pinched or trapped in clothing. Their bite is merely a defense reaction; when you're cleaning the garage you may stick your finger in the spider's area, or trap it. Wearing gloves would prevent bites.

Lastly, humans out-weigh and out-size spiders many thousand times and are much more likely to behave with murderous intent. It should be the spider who feels "fear" at our approach -- not us. (Perhaps that's why they run so fast).

Spiders can be ignored if their numbers are small and they stay in out of the way places. They primarily eat insects already present in homes, such as cupboard pests, silverfish, or clothes moths. Sometimes they eat each other or capture stray insect invaders such as rootweevils and blowflies. Spiders that are more visible, like the ones that get trapped in the tub or run up a wall, can be captured and released outside, vacuumed up, swatted flat, or sprayed with an insecticide. (Do not over-spray).

Usually spider activity declines by mid-October. Unless you continually introduce new spiders on firewood, household spiders will retire into obscurity for another year, quietly killing several times their weight in household insect pests and flies.

Because spiders inject a small amount of venom into their prey, they are all "poisonous." Some spiders, however, are known to be dangerously venomous to humans. Their poison has a severe effect on most humans. Most other spiders, if they are able to penetrate the skin, produce only a mild reaction varying from none, to that of a mosquito bite or wasp sting, unless the individual has an allergy to that particular venom. Consult a physician if pain and discomfort follow a spider bite.

The only dangerously venomous spider known to occur in Washington is the western black widow, Latrodectus hesperus. There are only a few, small, permanent populations of this spider in Snohomish County, but it is quite common in eastern Washington. Specimens are sometimes introduced to the west side on vehicles and in hay shipments but generally cannot establish permanent populations in our climate. Widows are shy, retiring spiders and bite only reluctantly, usually only when molested. A common local house species, Steatoda sp., is often mistaken for a black widow but has no red mark.

The much feared brown recluse spider, Loxosceles reclusa is not known to be established anywhere west of the Rocky mountains. Occasional news reports of bites by brown recluse spiders have never been verified with an actual spider specimen.

More common in the Puget Sound Area is Tegenaria agrestis, sometimes called the aggressive house spider. This spider sometimes bites with little provocation when cornered or threatened. T. agrestis is more commonly known as the "hobo spider" as it is commonly found along railroad tracks. Hobo spiders can cause a severe reaction in persons allergic to spider venom, with the allergic reaction being very similar to that of the brown recluse.

As in all spider bites, if you can trap the offending spider, your County Extension Office should be able to tell if it is one of the dangerous species.

You alone can select the methods that will solve your spider problem or your reaction to the problem Fortunately, there will always be spiders. The best solution is to manipulate the environment so the spiders don't live where you do. It is unrealistic to expect that spiders can be totally eliminated. On the other hand, one need not live with abundant spiders. If you can't live with your spiders, some of the following approaches can reduce their numbers:

1. Habitat modification: those spiders which are capable of moving indoors are ones which establish their webs in wood piles, junk piles, disused yard furniture or traps, trash bins, outdoor stairwells, window frames, porch superstructures, brick piles, or ventilation structures. Eliminating or keeping these sites relatively clean will help to keep spider populations low.
2. Structural modification: prevent spider entry by keeping doors and windows screened; by weatherstripping doors so there are no openings between the bottom of the door and the doorsill; closing gaps around water pipes under sinks; and sealing cracks and openings in the house.
3. Sanitation inside: Stored boxes, piles of magazines and other items in basements create ideal hiding places for spiders. Many live out their lives and die without ever being noticed. The old practice of spring and fall cleaning is a practical control measure. Vacuum behind and under furniture and book cases, along baseboards and corners and in storage areas.
4. Pesticides (inside): an aerosol bomb or fogger will reduce spiders, as well as fleas and other insects that are already present. It will not provide residual control for insect coming in later. The pesticide also may not penetrate inaccessible areas. Follow label directions.
5. Pesticides (outside): Cyfluthrin, bifenthrin, permethrin, tetramethrin or deltamethrin can be applied around the outside of doors, window, vents, outdoor stairwells or window wells, foundations, or cracks and openings. Spray only where needed. Be sure that the site, (indoor use, along foundations outside, etc.) is listed on the label. The product should also be labeled for spiders or nuisance pests.
For more information, see WSU Pest Sense at http://pep.wsu.edu/pestsense/
6. Exterminators: Professional pest control operators (PCO's) or exterminators will tackle the job for you. There are many approaches used by various companies.
7. Firewood: Spiders seek warmth and shelter in protected places like logs, under piles of rocks, bark and other debris. The wood pile is a choice winter residence. Many spiders ride inside on the firewood. Protect outside wood piles with covering. The more debris that falls on the wood, the more attractive the spiders find it. It isn't advisable to spray the wood pile. Pesticides with enough residual to keep spiders out could be toxic to handle, ant there is no information available on possible health effects of burning wood treated with pesticides.
8. New construction: if you are adding a room, building a house, or remodeling, consider treating the wall voids with relatively non-toxic (to humans) boric acid. This material is picked up on the spider's body and eaten when the spider grooms itself.

Usually, successful pest management requires a combination or blend of methods. Each situation may require a different combination of management strategies.

The most reliable way to distinguish major spider groups is by arrangement of the eyes on the "head" region of the spider. On the large spiders, this eye arrangement is readily visible. A hand lens or magnifier may make the job easier in some cases.

1. Eyes in 3 rows, arranged in 4, 2,2 pattern (Wolf spider & Jumping spider)

2. Eyes in 2 rows of 4 (most spiders)
3. Eyes in 3 pairs (Brown recluse and relatives)

Using the eye arrangement is much more accurate when trying to identify Brown Recluse spiders and spiders which have been squashed.

Prepared by Sharon J. Collman, County Extension Agent, Mr. Rod Crawford, Burke Museum, University of Washington and Dr. Art Antonelli, Washington State University Extension Puyallup. Slightly revised 12/03 . Photo by Dave Pehling.

Other Spider Sites:

The Hobo Spider Website

How to Identify (or misidentify) the Hobo Spider - PLS116 PDF file

The International Society of Arachnology

Spider Myths web site - U.W. Burke Museum

The Arachnology web site

Additional reading: Hobo Spider, a.k.a Aggressive House Spider by WSU entomologist, Todd Murray.

Spiders and Other Arachnids U.C. Riverside

WSU Publications Spiders, EB 1548: also available through your local WSU Extension Office for a nominal fee.

If you have additional questions contact your local WSU Extension office.

Link updated 12/10 Dave Pehling