The colony size gap that changes everything
If you take one number away from this page, make it this one. UC IPM puts yellowjacket colonies at between 1,500 and 15,000 individuals, and paper wasp colonies at 15 to 200. That is not a difference of degree. A paper wasp comb under an eave holds fewer wasps than a bad day at a picnic, and the colony defends only the comb itself. Someone standing three feet away is not being threatened. Treating one after dark is a genuinely small task. A yellowjacket colony at the top of that range is a different animal. Disturbing the entrance brings out a large fraction of the workforce, each of which can sting repeatedly, and they pursue rather than simply defending. That is why the same advice cannot cover both. The good news is that identification is easy without getting close. If you can see the individual hexagonal cells hanging in the open, you have the small colony. If all you can see is a hole with wasps going in and out, you have the large one, and nothing about that hole tells you whether the nest behind it holds two thousand wasps or ten.
The yellowjacket that nests in houses
Most yellowjacket problems in California are ground nests, but there is a specific reason Fresno homeowners find them in walls. UC IPM reports that the German yellowjacket is becoming more common in many urban areas of California, where it frequently nests in houses. It uses wall voids, attic corners, and spaces behind soffits, entering through a gap in siding, an unscreened vent, or an opening around a pipe or fixture. What makes these colonies different is what happens when they are handled badly. A ground nest that gets a poor treatment stays in the ground. A wall colony that finds its entrance blocked, or that is disturbed by spraying at the gap, will look for another way out, and the interior wall surface is softer than the exterior. People end up with wasps in a bedroom rather than in the yard. So the sequence for a wall colony is fixed. Treat the opening at night with a dust, wait until traffic has stopped completely over several days, and only then seal it. Never reverse those steps, and never seal first because the wasps are annoying.
Fruit, harvest, and the late-season shift
Around an agricultural city, the fall wasp problem has an extra ingredient that most places do not have in the same quantity. By late summer, a colony has largely stopped raising brood, and the workers forage for themselves, which means sugar. Ripening fruit, split fruit still on the branch, and drops rotting under a tree are all concentrated sugar in exactly the weeks the colony is at maximum size. A backyard with a few fruit trees can support heavy wasp traffic without any nest being on the property at all. That matters practically because it explains a frustrating experience: treating a nest and still having wasps everywhere. If the food source is a fruit tree, foragers from colonies elsewhere in the neighborhood will keep arriving. The fixes are ordinary. Pick fruit as it ripens rather than letting it split, clear drops daily during the heaviest weeks, and keep green waste containers latched. If a gathering is coming up, put lure traps at the far edges of the yard several days ahead, and keep them away from where people will be sitting.
Why the Fresno season starts so early
Wasp advice written for the rest of the country tells you to start looking in May. In the Central Valley that is two or three months late. UC IPM describes California queens emerging in late winter to early spring, and with average winter lows near 38 degrees, Fresno gets that early start reliably. A queen that comes out in February has a long stretch of solo building ahead of her before the first workers appear, and during that window a nest is a few cells and one insect. That is the cheapest wasp control available anywhere. A comb removed from an eave in February prevents a colony that would otherwise hold hundreds by September, and it takes a pole and a bucket rather than a treatment. By late summer the same source notes that colonies grow more slowly or cease growth, which sounds reassuring but is not. The nest has already reached its maximum size at that point, and its workers have switched to scavenging, so the peak nuisance and the peak risk both fall after the growth has stopped. The practical calendar here: inspect from February, act on anything you find, and treat late-season nests as professional work.
What a Fresno quote should actually cover
Wasp work is priced after a look at the property, which is reasonable, but the number should account for a defined scope. Ask whether locating the nest is included. If the wasps are scavenging and no nest has been found, tracing them may take a separate visit, and it may end in a trapping program rather than a treatment. Ask whether a follow-up is included. Colonies in walls and under slabs sometimes need a second application, and finding out later that the return trip is billable is a common complaint. Ask what happens to the nest itself. For a comb under an eave, removal is trivial. For a colony inside a wall, ask directly whether removing the nest material would mean opening the wall, and who repairs it. Ask whether sealing the entry is part of the job, since treatment without sealing leaves the same cavity open for next spring. And ask what happens if a second nest turns up during the walkthrough, which is common on lots with outbuildings and fruit trees. Get those five answers in writing before you compare prices.
When leaving a nest alone is the right call
Not every nest needs treating, and a company that says so is being straight with you. A bald-faced hornet nest high in a shade tree at the back of a lot, well away from where anyone walks, is a reasonable candidate for leaving alone. Aerial nests in trees are routinely left to die back on their own as the season ends, and the paper is not reused afterward. A small paper wasp comb on a side of the house nobody uses is another. With 15 to 200 wasps and a defended radius measured in inches, it is a low-risk neighbor if you are not reaching past it. What changes the answer is proximity and people. A nest near a door, a gate, a play area, or a spot where someone works regularly should be dealt with regardless of species, because ordinary movement counts as disturbance to the colony. And allergy overrides all of it. If someone in the household has had a systemic reaction to a sting, no nest on the property qualifies as one to watch and wait on, however far from the house it looks.