How big is that nest, really?
Guessing colony size from the outside of a nest is unreliable, which is why Penn State's published figures are the most useful thing you can carry into this decision. A paper wasp colony is typically a few dozen adults but can grow to over 200. Bald-faced hornets reach upwards of 300 individuals in a single gray sphere. European hornets peak at 200 to 400 workers, and large nests can hold roughly 1,000. Yellowjacket colonies, Penn State says, run anywhere from a few hundred to thousands. Those numbers translate directly into risk. A dozen paper wasps on an open comb can be treated and walked away from. Three hundred bald-faced hornets pouring out of an enclosed nest is a situation you cannot outrun on a ladder. Size also changes across the season. The same nest that looked trivial in June may be at four or five times that number by early September, which is why the honest answer to "should I handle this myself" depends heavily on what month you are asking in.
Yellowjackets in walls and hillsides
German and eastern yellowjackets are the Pittsburgh species most likely to put someone in an urgent care. Neither builds where you can see it. German yellowjackets favor wall voids, attics, and hollow porch columns. Eastern yellowjackets go underground, and an abandoned rodent burrow against a foundation or the base of a retaining wall is a ready-made cavity. On hillside properties this matters more than usual. Sloped yards, terraced beds, and stone walls give ground-nesting yellowjackets far more options than flat turf does, and they put the entrance at foot level along paths people use. The warning sign is traffic, not the nest. Watch a suspect spot from ten or fifteen feet during midmorning. Yellowjackets returning to a colony fly a consistent line to a consistent hole, and dozens per minute passing through one opening means an established nest. Mark it from a distance with a stake, keep the mower and trimmer away, and treat after dark rather than during the day.
A month-by-month wasp calendar for Pittsburgh
May: Penn State places paper wasp nest establishment in this month. Queens work alone, nests are tiny, and prevention is cheap. Spend fifteen minutes a week walking the eaves. June and July: the first workers take over hunting and the queen becomes a full-time egg layer. Colonies grow quietly. This is the right stretch for exclusion work, capping railings and screening vents, because you are not working around a defensive colony yet. August and early September: peak numbers and peak defensiveness. Foragers shift toward sugar, which is why they start showing up at bins and drinks. Penn State puts European hornet nests at their maximum around mid-September. Late September: paper wasp colonies are essentially finished. Activity drops sharply. October onward: new queens have left to overwinter and the first hard frosts kill the rest. Pittsburgh's winter lows near 22F are more than enough. Old nests are empty and safe to take down.
What the first visit should include
A useful first visit starts with a walk around the whole building rather than a beeline to the nest you called about. Paper wasps commonly build several combs on one house, and treating one while three others stay active is a wasted trip. Someone should be checking porch ceilings, rails, window ledges, soffit and gable vents, hollow columns, shrubs at eye level, and the ground along foundations and walls. If the nest is hidden, part of the visit is diagnostic. Finding where wasps enter takes standing back and watching flight lines, and on a narrow lot that may mean going next door or waiting for a time of day when the light is better. Then there is timing. Anyone describing a plan to treat a full colony at two in the afternoon is describing a partial job. Ask whether they will come back after dark. Ask, too, what the price covers: locating, treating, verifying the colony is dead, and sealing the opening are four distinct pieces of work, and companies bundle them differently.
Renters, landlords, and nests on the building
In a Pittsburgh rental, a wasp nest attached to the structure is normally the owner's responsibility, because it involves the building rather than housekeeping. Report it the day you find it, in writing, with a photo and a precise location. A dated record is what makes the timeline clear if the situation drags. Ask specifically about sealing. Treating a wall-void colony without closing the entry afterward means the same gap is available to next spring's queen, and older buildings in this city have plenty of opened trim joints and gaps behind porch framing to offer. Landlords have their own reasons to move quickly. A large yellowjacket colony in a wall can soak insulation and stain drywall, and a nest at a shared entry exposes every tenant and anyone delivering to the door. In a multi-unit building, treat the exterior as one job rather than three, since a single cavity often runs behind more than one apartment and a partial treatment just shifts the traffic.
When a sting becomes a medical emergency
Most stings hurt, swell for a day, and are finished. The exceptions are worth recognizing on sight rather than looking up afterward. Call 911 if someone develops hives spreading away from the sting site, swelling of the lips, tongue, or throat, dizziness or fainting, or any difficulty breathing. Those are signs of a systemic reaction, and they can progress quickly. Multiple stings from a disturbed ground or hornet nest also warrant medical attention even without an allergy history, simply because of the venom load. The scale of this risk is well documented. The American College of Allergy, Asthma and Immunology puts potentially life-threatening reactions to insect venom at 0.4 to 0.8 percent of children and roughly 3 percent of adults, so adults are the more affected group. The University of Kentucky estimates about two million Americans are hypersensitive to stinging insect venom, which is close to one household in a hundred. If that describes yours, nobody in the house should be attempting nest removal.