Spiders often cause concern, but in Oregon, only a few species pose a significant health risk to humans. Most spiders found across the state are harmless and play an important role in controlling insect populations. Understanding the distinction between common spiders and medically significant ones can help alleviate worry.
The Medically Significant Spiders in Oregon
The Western Black Widow, Latrodectus hesperus, is the main medically significant spider in Oregon. Female black widows are shiny black, 14-16 mm, with a red, yellow, or white hourglass mark on their abdomen. Males are about half this size and tend to be tan with lighter stripes. They build irregular, messy webs in low-lying areas like woodpiles, garages, and dark corners, especially in rural and suburban settings. While present throughout the state, they are more common in Eastern and Southwestern Oregon, though they can occasionally be found in the Willamette Valley.
The Western Black Widow’s venom is neurotoxic. A bite may initially feel like a sharp pinprick or go unnoticed, but symptoms can develop within an hour. These often include localized pain, redness, and swelling, which may spread to the abdomen, back, or chest, with muscle cramps and spasms. Other reactions include nausea, vomiting, sweating, headache, chills, and restlessness, potentially lasting several days. Bites are uncommon and typically occur defensively when the spider feels threatened or is accidentally pressed against skin.
The Brown Recluse spider, Loxosceles reclusa, is often a source of misconception. This species is not native or established in Oregon. Sightings in Oregon are almost always misidentifications, often confused with other common spiders like the Hobo spider. It is primarily found in the south-central United States; its presence in Oregon is usually limited to transported instances.
Common Spiders Often Mistaken for Dangerous Ones
Many common Oregon spiders are often misidentified as dangerous, despite posing minimal threat. The Hobo spider, Eratigena agrestis, is a common example, widely distributed in the Pacific Northwest after its introduction from Europe. These spiders build funnel-shaped webs and are typically brown. Despite a past reputation, current evidence indicates Hobo spider bites are not medically significant and do not cause severe tissue damage. A bite may result in minor localized pain, redness, swelling, or twitching, usually resolving within a few hours to a couple of days.
The Giant House spider, Eratigena atrica, is another large spider often found in Oregon homes, reaching a leg span of up to 75 mm. These brown spiders are not aggressive, and their bites are rare, causing little to no toxicity. When a bite occurs, symptoms are mild, comparable to a bee sting, producing minor localized irritation, pain, swelling, and redness.
Wolf spiders (Hogna genus) are large, hairy, fast-moving spiders common in Oregon. Unlike many spiders, they do not build webs to catch prey; instead, they actively hunt on the ground. While their size can be intimidating, wolf spider bites are not medically significant. A bite may cause localized pain, throbbing, swelling, and redness, similar to a bee or wasp sting, usually resolving within a few days.
What to Do About Spider Bites
For most spider bites, basic first aid can help manage symptoms. Clean the bite area gently with mild soap and water. Apply a cold compress (e.g., ice pack wrapped in cloth) for 15 minutes each hour to reduce pain and swelling. Elevating the affected area can also minimize swelling. Over-the-counter pain relievers can alleviate discomfort, and antihistamines may be used for itching.
Seek medical attention if a black widow spider bite is suspected, or if severe symptoms develop. These include severe pain, widespread muscle cramps, nausea, or vomiting. Signs of infection, such as increasing redness, warmth, or pus spreading from the bite site, also warrant professional evaluation. Any signs of an allergic reaction, such as difficulty breathing or swallowing, facial swelling, or a widespread rash, require immediate medical care.
To minimize encounters with spiders in and around the home, several preventive measures can be taken:
Sealing cracks and openings in foundations, walls, and around pipes can limit entry points.
Repairing damaged window and door screens and installing door sweeps can help exclude spiders.
Clearing clutter like woodpiles, leaf debris, and dense vegetation away from the house removes potential hiding spots.
Indoors, regularly shaking out clothes and shoes before wearing them can help prevent accidental bites.