Black widow spiders are found in Oregon, primarily the Western Black Widow (Latrodectus hesperus). While they are present statewide, their populations are more prevalent in southwestern and eastern Oregon. These spiders can also be found in northwestern Oregon, often on south-facing slopes bare of dense trees, and occasionally within homes in the Willamette Valley.
The Western Black Widow is Oregon’s most medically significant spider due to its neurotoxic venom. However, the amount of venom injected during a bite is usually not enough to cause a severe reaction in most people.
Identifying a Black Widow
Identifying a Western Black Widow primarily involves the mature female. These spiders are shiny black, about 0.5 inches (12-16 mm) long, with a leg span of 1.5 to 1.97 inches.
A distinguishing feature is the rounded, globular abdomen, which usually displays a red or orange hourglass-shaped marking on its underside. This hourglass shape can sometimes vary, appearing as unconnected dots or a faded mark.
Males are much smaller than females, light brown with pale diagonal stripes or red spots. Immature spiders are lighter, often olive or gray with white or yellow stripes. Only the mature female possesses venom potent enough to be a concern to humans.
Where Black Widows Live and Behave
Western Black Widows establish their webs in dark, undisturbed locations, both indoors and outdoors. Common outdoor habitats include woodpiles, rock piles, under stones, and meter/sprinkler valve boxes. Indoors, they may be found in basements, garages, sheds, and crawl spaces, particularly in corners or cluttered areas.
Their webs are irregular, sticky, and “cobweb-like,” lacking the organized patterns of other spider webs. Black widows are nocturnal and reclusive, generally avoiding human activity. They are not aggressive and only bite if threatened, such as when accidentally pressed against skin or when their egg sac is disturbed.
Understanding and Responding to a Bite
A black widow bite may initially feel like a pinprick, sometimes going unnoticed. Symptoms often develop within minutes to several hours. These can include severe muscle pain and cramping, which may spread from the bite site to the abdomen, back, or chest. Other reported symptoms are nausea, vomiting, sweating, headache, increased heart rate, and fever or chills.
While black widow bites are rarely fatal, particularly for healthy adults, they can be medically significant and require prompt attention. Children, the elderly, and individuals with compromised immune systems are more susceptible to severe complications.
If a bite is suspected, clean the area with mild soap and water, apply a cold compress or ice pack to reduce pain and swelling, and elevate the affected limb. Seek medical attention immediately for any suspected black widow bite, and if possible, safely bring the spider for identification. Medical treatment typically focuses on managing symptoms, though antivenom may be administered in severe cases.