Spiders can be creepy, but they are an important part of our ecosystem and provide pest control by catching and eating other insects like house flies and mosquitoes. When temperatures start to cool, spiders may migrate into garages and homes in search of warmth and shelter.
Spiders rarely bite people. Unexplainable wounds are often misdiagnosed as spider bites, which can result in a condition not being treated properly and may lead to serious complications. Medical conditions commonly misdiagnosed as spider bites include methicillin-resistant Staphylococcus aureus (MRSA), other bacterial infections, viral or fungal infections, as well as chemical or thermal burns.
Are there venomous spiders in Washington?
Almost all spiders have poison glands, but very few spiders are harmful to people. There are two spiders in Washington of medical significance: the black widow spider and the yellow sac spider. Spiders are usually not aggressive, but bites can happen when spiders become trapped against the skin or accidentally disturbed. Spider bites can result in allergic reactions; also, secondary infections can occur if wounds are not treated appropriately.
How to Prevent Spider Bites and Keep Spiders Out of Your House
- Brush spiders off you, don't crush them. Bites are more likely if a spider is squished or pressed against your skin.
- Check and shake out clothing and shoes before putting them on, particularly if they have been stored in a garage, shed, or barn.
- Wear protective clothing like long-sleeved shirts, long pants, hat, gloves, and shoes when handling stored firewood or boxes, or when cleaning sheds, garages, barns, basements, attics, and crawl spaces.
- Use tight-fitting screens on windows and doors. Use caulk or other sealants to seal small cracks and openings.
- Vacuum regularly, particularly around door and window frames, behind furniture, and along ceiling and floor edges.
- Clear away clutter like old furniture, boxes, or clothes that sit in undisturbed areas of your home or garage.
- Move beds away from the walls, remove bed skirts, and move out items stored under the bed.
- Inspect firewood, potted plants, and other objects before bringing them inside your house.
- Keep wood piles, rock piles, shrubbery, and other objects away from the outer walls of your house.
- Use a broom to move spiders and their webs from the foundation, eaves, windows, and door frames to areas away from your house.
What to Do if You're Bitten by a Spider
- Seek medical attention immediately if you suspect the bite was from a black widow. If possible, bring the spider with you. Identifying the type of spider can help in medical treatment.
- Wash the bite area with soap and water.
- Place ice on the bite area to reduce swelling and provide pain relief.
- Wrap a stretchable bandage around the bite area to help reduce swelling further. Loosen the bandage if it feels too tight or causes throbbing.
- Elevate the bite area if possible.
- Do not attempt to remove venom.
- If symptoms don't improve, seek medical attention.
Allergic Reactions to Spider Bites
Most spider bites cause minor and temporary symptoms, but some people have severe allergic reactions, including anaphylactic shock. This can occur quickly and lead to rapid death if not treated immediately.
Immediately seek medical attention for symptoms of anaphylaxis, which include:
- Chest pain.
- Face or mouth swelling.
- Difficulty swallowing or breathing.
- Fainting or lightheadedness.
- Rash or flushing.
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.
Possible symptoms resulting from a spider bite include:
- Itching or rash.
- Pain radiating from the bite, muscle pain, or muscle cramping.
- Reddish to purplish color or blistering.
- Sweating, fever, or chills.
- Difficulty breathing.
- Headache.
- Nausea and vomiting.
- Anxiety or restlessness.
- High blood pressure.
Black widow spider bites are a significant health risk for young people, the elderly, and those with high blood pressure or compromised immune system. Black widow bites don't cause conspicuous swelling, necrosis, or deterioration of tissue around the bite.
Medically Important Spiders in Washington State
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 half an inch long.
Black widow spiders prefer dark undisturbed areas like woodpiles, hay bales, water meter boxes, fences, and under eaves. Indoors, they may be found in undisturbed, cluttered areas like basements, crawl spaces, or unused areas of garages. Female black widows build messy-looking webs in or behind objects in secluded and protected locations.
False Black Widow Spiders
False black widow spiders (Steatoda grossa) closely resemble female black widow spiders and are common in Washington. However, the false black widow spider is all black and doesn't have red markings on their abdomen. False black widow spider bites do happen, but their venom is much less toxic than a black widow's.
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 an inch long. Yellow sac spiders can be yellow, white, or even greenish, and their legs and upper body are darker than their abdomen. These spiders can bite when trapped against a person's skin in clothing or bedding.
Their body is small, about a quarter to a half an inch long. Yellow sac spiders can be yellow, white, or even greenish, and their legs and upper body are darker than their abdomen. These spiders can bite when trapped against a person's skin in clothing or bedding. 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.
Other Spiders
Hobo Spider
Hobo spiders (Eratigena agrestis) are not considered dangerous as previously thought. Despite their other common name, the aggressive house spider, hobo spiders are shy, retiring, and reluctant biters. They are not aggressive and try to escape when disturbed. Hobo spiders can be found throughout Washington. There is no evidence hobo spider venom has caused skin necrosis or necrotic wounds in people.
Brown Recluse Spider
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 commonly found in southern regions of the United States.
Resources
Widow Spiders and Their Relatives, University of California
Brown Recluse and Other Recluse Spiders. University of California
Arachnology & Entomology Collections, Burke Museum
Homeowner Guide to Spiders Around the Home and Yard, University of Idaho (PDF)
Content Source: Zoonotic Disease Program