Pennsylvania is home to a wide variety of wasps, from social species that build large colonies to solitary ones that nest alone in the ground or in mud structures. Understanding which species you’re looking at helps you gauge the actual risk, since many of the biggest, scariest-looking wasps in the state are essentially harmless. Here’s a breakdown of the species you’re most likely to encounter.
Yellowjackets
Yellowjackets are the wasps most Pennsylvanians think of first, and for good reason. Ten species of yellowjackets live in eastern North America, and several are common across the state. They’re relatively small, topping out around half an inch, with bold yellow and black banding on the abdomen. In flight, they hold their legs tight against their bodies, giving them a compact, fast-moving silhouette.
Most yellowjackets nest underground, which is why you might stumble on a colony while mowing the lawn or walking through a park. Some species will also nest in enclosed aerial spaces like wall voids or attic cavities. Their nests are wrapped in a papery envelope, so you won’t see open cells the way you would with a paper wasp nest. Colonies can grow to several hundred workers by midsummer, and yellowjackets become noticeably more aggressive in late summer and early fall as food sources dry up. They’re attracted to sugary drinks, fruit, and meat at outdoor gatherings, which is when most stings happen.
One species worth noting is the southern yellowjacket. Queens of this species can reach about 0.65 inches, noticeably larger than other yellowjackets, and are sometimes mistaken for hornets when they emerge in spring to start new colonies.
Paper Wasps
Paper wasps are slimmer and more elongated than yellowjackets, with a narrow “waist” and long legs that dangle visibly during flight. Pennsylvania has both native paper wasps and the European paper wasp, an introduced species that has become extremely common.
The European paper wasp is black with prominent yellow markings and is frequently mistaken for a yellowjacket. The key differences: it’s larger, has a thinner waist, and its antennae are tipped with orange rather than being solid black. Native paper wasps tend to be darker, with coloring that runs toward browns, blacks, and dark reds. A few native species are entirely dark red.
Paper wasp nests are easy to identify. They look like small upside-down umbrellas with open, visible cells hanging from a single stalk. You’ll find them under eaves, inside light fixtures, in attics, inside grills that haven’t been used in a while, and in wall voids. Paper wasps are less aggressive than yellowjackets or hornets and typically sting only when they feel the nest is directly threatened. Interestingly, wasps sting about twice as hard as bees but inject roughly one-tenth the venom per sting.
European Hornets
The European hornet is the largest social wasp in Pennsylvania. Workers reach about an inch long, and queens can hit 1.3 inches. Their coloring is distinctive: a red and yellow head, a reddish-brown midsection, and an abdomen that’s brown near the front fading to yellow toward the rear with brown teardrop-shaped markings. They’re the species most commonly mistaken for the northern giant hornet (formerly called the “murder hornet”), though the two aren’t closely related and the northern giant hornet has never been found in Pennsylvania or anywhere in eastern North America.
European hornets nest in protected aerial cavities, particularly hollows inside large standing trees and sometimes inside the wall voids of houses. Unlike yellowjackets, they don’t nest in the ground, and unlike bald-faced hornets, they don’t build exposed nests hanging from branches. They’re the only nocturnal wasp in Pennsylvania, so if you see a large wasp buzzing around your porch light at night, it’s almost certainly a European hornet.
These hornets are predators for most of the year, hunting grasshoppers, flies, and even yellowjackets. In fall, they shift toward sugar and carbohydrates, feeding on fallen apples and pears and sometimes stripping bark from lilac bushes to get at the sap.
Bald-Faced Hornets
Despite the name, bald-faced hornets are technically a type of yellowjacket rather than a true hornet. They’re easy to identify: black bodies with striking white (not yellow) markings on the face and abdomen. They’re smaller than European hornets but still imposing, and they serve as important predators of caterpillars, flies, and other soft-bodied insects.
Their nests are the large, gray, football-shaped paper structures you sometimes see hanging from tree limbs, house eaves, or utility poles. These enclosed nests can grow quite large over the course of a summer. Bald-faced hornets are defensive of their nests and will sting if you get too close, so give any active nest a wide berth.
Cicada Killers
If you’ve ever seen a wasp the size of your thumb hovering over your lawn, it was probably an eastern cicada killer. These solitary wasps are yellow and black, similar in size to a northern giant hornet, and they look genuinely terrifying. They’re not.
Cicada killers dig burrows in well-drained, sunny soil, with entrance holes about 1.5 inches wide leading to tunnels 12 to 18 inches long. Females hunt cicadas, paralyze them with a sting, and drag them into underground cells where they lay their eggs. Each female stocks about four cells with one to three paralyzed cicadas apiece. Multiple females often nest near each other, creating aggregations of a few dozen to over a hundred burrows that can persist in the same spot for years.
Most of the cicada killers you see flying around are males patrolling the nesting area. They’ll dive-bomb you and hover in your face, but males can’t sting at all. Females have stingers but don’t defend their burrows and will only sting if you physically grab them. These wasps are harmless neighbors.
Mud Daubers
Mud daubers are long, slender solitary wasps with a distinctive thread-like waist. Three types are common in Pennsylvania, and each has a different approach to nest building.
- Black and yellow mud daubers build cylindrical mud cells, then plaster them over with more mud to create a smooth nest roughly the size of a fist.
- Organ-pipe mud daubers are robust, all-black wasps that construct parallel tubes of mud on smooth surfaces like walls and the undersides of bridges, resembling small pipe organs.
- Blue mud daubers are metallic blue-black with blue wings. They skip the construction entirely and instead take over the abandoned nests of black and yellow mud daubers.
All three types feed their larvae a diet of spiders that the female catches and paralyzes. Mud daubers do not defend their nests and are extremely unlikely to sting. You can safely observe them working from just a few feet away.
Seasonal Activity in Pennsylvania
Social wasp colonies in Pennsylvania follow a predictable annual cycle. Queen wasps emerge from underground overwintering sites in spring and begin establishing nests in May. The colony grows through summer, reaching peak size by late July or August, with some species producing several hundred workers. New queens and males are produced in late summer, and mating happens in fall. By the end of September, most colonies have died off entirely. Only newly mated queens survive, burrowing underground to wait out winter.
The practical takeaway: wasps become more defensive as summer turns to fall, precisely because food is getting scarce and the colony is winding down. August and September are the months when you’re most likely to have a hostile encounter, especially around outdoor food. If you need to remove a nest near your home, doing it after dark when wasps are least active is the safest approach. Solitary species like cicada killers and mud daubers are active during roughly the same months but pose virtually no sting risk at any point in the season.
What About “Murder Hornets”?
Northern giant hornets do not occur in Pennsylvania or anywhere in eastern North America. As of the most recent monitoring, they have only been confirmed in Washington state and on Vancouver Island in British Columbia. The large wasps Pennsylvanians sometimes mistake for them are almost always European hornets or cicada killers, both of which are similar in size and coloring. If you think you’ve spotted one, check the antennae color and nest location. An orange-tipped antenna points to a European paper wasp. A wasp hovering over lawn burrows is a cicada killer. And a large wasp at your porch light at night is a European hornet.