Spiders

Are there any venomous spiders in Washington?

The real concern is whether or not the spider is venomous enough to present a danger. Nearly all spiders are venomous to some extent, yet very few are harmful to people. There are two spiders of medical significance in Washington, the black widow spider and the yellow sac spider. Although spiders usually are not aggressive, bites can happen when they become trapped or accidentally disturbed.

How do I prevent spider bites?

What should I do if I'm bitten by a spider?

What are the symptoms of a spider bite?

Symptoms associated with spider bites can vary from minor to severe. Although extremely rare, death can occur in severe cases. Most spider bites cause minor and temporary symptoms. Possible symptoms resulting from a spider bite include:

Black widow spider bites are a significant health risk for the very young, elderly, and those with high blood pressure and compromised immune system.

Misdiagnosis of unexplained lesions as spider bites frequently occurs. Medical conditions misdiagnosed as spider bites include methicillin-resistant Staphylococcus aureus (MRSA) and other bacterial infections, as well as viral and fungal infections and chemical and thermal burns.

Can people be allergic to spider venom?

Yes. Some people have severe allergic reactions to spider bites, including anaphylactic shock. This can occur quickly and lead to rapid death if not treated quickly.

Immediately seek medical attention for symptoms of anaphylaxis. They include:

How do I recognize a black widow spider? Where can they be found?

Black Widow Spider

Black Widow Spider

Black widow spiders (Latrodectus species) are common to eastern Washington. A few small populations of black widows exist in western Washington. Adult female black widows have dangerous venom, but will often try to escape rather than bite, unless guarding their eggs. Female black widows are normally shiny black with a red hourglass marking on the underside of their abdomen. The marking can also be yellowish-orange and its shape can vary, resembling an hourglass, two marks, or a single dot. The body of an adult female is relatively large, about a half-inch long.

Black widow spiders prefer dark undisturbed areas, such as woodpiles, bales of hay, water meter boxes, under eaves, and fences. Indoors, they may be found in undisturbed, cluttered areas in basements, crawl spaces, or unused areas of garages. Female black widows build messy-looking webs in or behind objects in secluded and protected locations.

Are there other spiders that resemble a black widow spider?

Yes. False black widow spiders (Steatoda grossa) closely resemble female black widow spiders, and are common in Washington. However, the false black widow spider are all black and do not have the red markings on their abdomen. False black widow spider bites do happen, but their venom is much less toxic than a black widow's.

How do I recognize a yellow sac spider? Where can they be found?

Yellow Sac Spider

Yellow Sac Spider

Yellow sac spiders (Cheiracanthium species) are found in eastern Washington and in the Seattle area. Their body is small, about a quarter- to a half-inch long. Yellow sac spiders can be yellow, white, or even greenish, and their legs and upper body darker than the abdomen. These spiders can bite when trapped against a person's skin in clothing or bedding.

Yellow sac spiders are mainly garden-dwellers in the warm season, but can make their way indoors in the fall. They move quickly, and are good climbers. Indoors, they are often found along walls and ceilings. Instead of webs, yellow sac spiders build small silken sacs where they hide during the daytime. Outdoors, the sacs may be found under planters, firewood, and in curled up leaves. In homes, the sacs can be found in the corners of walls and ceilings, behind shelves and pictures, and along windowsills.

What about the hobo spider? Isn't their bite a health concern?

Hobo spiders (Eratigena agrestis) are not considered dangerous as once believed. Hobo spiders are shy, retiring, and reluctant biters, despite their other common name, the aggressive house spider. They are not aggressive and try to escape when disturbed. Hobo spiders can be found throughout Washington. There is no evidence that hobo spider venom has caused skin necrosis or necrotic wounds in people.

What about the brown recluse spider? Isn't their bite a health concern?

Fortunately, brown recluse spiders (Loxosceles species) do not live in Washington. The venom from these spiders can cause a severe necrotic wound that requires medical attention. Brown recluse spiders are most commonly found in the midwest and southern regions of the United States.

Resources

Venomous Spiders, CDC

Widow Spiders and Their Relatives, University of California

Brown Recluse and Other Recluse Spiders. University of California

Spider Research, UC Riverside

Arachnology & Entomology Collections, Burke Museum

Homeowner Guide to Spiders Around the Home and Yard, University of Idaho (PDF)

Hobo Spiders in Idaho, University of Idaho (PDF)