Pennsylvania has only one truly dangerous spider species with an established presence: the black widow. Brown recluse spiders, the other species people worry about most, are not native to the state and show up only as rare hitchhikers in shipped boxes or moving containers. The vast majority of Pennsylvania’s spiders, including many large and intimidating species, are harmless to humans.
Black Widows: PA’s Only Established Dangerous Spider
The southern black widow is found throughout Pennsylvania, and the northern black widow is likely present as well. The female is the one to watch for: shiny, jet black, with the signature orange-to-red hourglass marking on the underside of her abdomen. Some females also have up to four red dots on top. Females measure 8 to 13 millimeters in body length, or roughly 25 to 35 millimeters with legs extended, about the size of a nickel including the legs. Males are much smaller (4 to 6 millimeters) and lack fangs large enough to pierce human skin, so bites come almost entirely from adult females.
Black widows prefer dark, undisturbed spots: under rocks, inside woodpiles, in vacant rodent burrows, and in the corners of barns, garages, and sheds. Their webs look messy and disorganized compared to the tidy designs of garden spiders. Females are most defensive during summer, when they’re guarding egg sacs. That’s when the majority of bites occur.
What a Black Widow Bite Feels Like
The bite itself feels like a sharp pinprick, followed by dull numbness around the site. You may notice tiny red fang marks, mild swelling, or a small blister. The skin around the bite can turn bluish-gray. None of that is the real problem.
Black widow venom targets nerve endings in your muscles. Within minutes to hours, it can cause severe, bodywide muscle pain and cramping, especially in the abdomen, shoulders, chest, and back. Other symptoms include headache, nausea, excessive sweating, fever, chills, trouble breathing, and swollen or droopy eyes. These systemic symptoms are what distinguish a widow bite from the bites of other spiders. With prompt medical treatment, most people recover fully within 24 to 48 hours. Long-term pain or muscle spasms are rare.
Brown Recluse Spiders Are Not Established in PA
This is the spider that generates the most unnecessary fear in Pennsylvania. Brown recluse spiders are established in 16 states, mostly in the south-central U.S.: Alabama, Arkansas, Georgia, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Mississippi, Missouri, Nebraska, Ohio, Oklahoma, Tennessee, and Texas. Pennsylvania is not on that list.
Isolated occurrences have been documented in the state, but these are spiders accidentally transported in boxes or furniture from regions where they’re native. Outside their home range, brown recluses are restricted to the buildings they arrived in. They don’t spread outdoors or establish breeding populations. The risk of being bitten by one in Pennsylvania is virtually nonexistent. If you’ve found a brown spider in your house and suspect it’s a recluse, it’s far more likely to be a wolf spider, a funnel weaver, or one of several other common brown spiders in the state.
Yellow Sac Spiders: A Minor but Real Concern
Yellow sac spiders are probably responsible for more human bites than any other type of spider, and two species live in Pennsylvania: the agrarian sac spider and the longlegged sac spider. These are small, pale yellowish spiders that build silken tube-like retreats in corners of ceilings, behind picture frames, and in folded clothing. The longlegged sac spider lives indoors year-round and has been observed crawling across skin and biting without provocation.
Most sac spider bites are relatively painless and don’t cause serious problems. For the more potent agrarian sac spider, or for people sensitive to the venom of either species, the bite can burn for up to an hour. A rash and blistering may develop over the next one to ten hours. Some people experience mild systemic symptoms like fever, muscle cramps, and nausea, similar to a very mild version of a black widow bite. A small ulcerated area can form at the bite site, but it typically heals without scarring.
Common Spiders That Look Scary but Aren’t
Pennsylvania is home to dozens of spider species that regularly alarm homeowners but pose no real threat. Knowing what they look like saves you unnecessary worry.
- Wolf spiders are large, fast, and brown, which is why they’re frequently mistaken for brown recluses. They hunt on the ground instead of building webs and often wander into basements and garages. Their bite is comparable to a bee sting.
- Fishing spiders are among the largest spiders in the state, with leg spans that can exceed three inches. They live near water and sometimes show up in cabins and lake houses. Despite their size, they’re not medically significant.
- False black widows are dark, round-bodied cobweb weavers that share the same family as true black widows. They lack the red hourglass marking. Their bites may cause mild, localized pain but nothing approaching the systemic effects of a real widow.
- Woodlouse hunters have large, prominent fangs and a reddish-brown body that makes them look menacing. They hunt pill bugs and can deliver a painful but harmless bite if handled.
- Parson spiders are dark, fast-moving ground spiders often found in homes. They’re sometimes confused with brown recluses because of their brown coloring, but they have a distinctive white marking on their abdomen and are not dangerous.
- Grass spiders and barn funnel weavers build funnel-shaped webs in grass, window wells, and basement corners. They’re brown with striped markings and are completely harmless.
Jumping spiders, orbweavers like the large yellow garden spider, and cellar spiders (the long-legged spiders dangling in your basement) round out the list of species you’ll encounter regularly. None require medical attention if they bite.
What to Do if You’re Bitten
For any spider bite, clean the wound with mild soap and water, apply antibiotic ointment, and use a cool compress for 15 minutes each hour to reduce pain and swelling. Elevate the area if you can, and take an over-the-counter pain reliever or antihistamine as needed for pain or itching. Watch the bite over the following days for signs of worsening redness, spreading warmth, or infection.
If you suspect a black widow bite, particularly if you develop muscle cramping that spreads beyond the bite area, get medical attention promptly. Antivenom is available for severe cases. Try to note what the spider looked like or, if you can safely capture it, bring it with you. Most spider bites in Pennsylvania, though, come from harmless species and resolve on their own within a few days.