Why colonies here can outlive their season
Almost every wasp guide in the country tells you the same thing: the colony dies at frost and the nest is never reused. That guidance does not transfer cleanly to this coast. UC IPM is explicit that normally yellowjacket and paper wasp colonies live only one season, but that in very mild winters, or in coastal California south of San Francisco, some yellowjacket colonies survive for several years and become quite large. San Diego, with average winter lows around 49 degrees, is about as far inside that exception as a place can be. The consequences are practical. A colony entering its second year does not restart from a single queen, so it reaches serious size months earlier in the year. A cavity that has held a multi year nest accumulates a large volume of paper, and clearing it may involve opening construction rather than reaching in. So watch for winter activity. If wasps are still moving in and out of an opening in December or January, treat it as a live colony rather than assuming it is leftover motion, and get it inspected before spring pushes it forward again.
Where nests turn up around a San Diego house
Start with the two categories, because they call for different tools. Exposed nests are the ones you can point at. Paper wasp combs show up under eaves, along patio cover beams, under stair rails, and inside hollow things: downspouts, pipe ends, umbrella poles, and the housing of anything left outdoors all winter. Concealed nests are the ones that matter more. Yellowjackets get into wall cavities through stucco cracks, weep openings, utility penetrations, and gaps where a roof meets a wall. On slopes and canyon edges they use soil cavities and old burrows. A slab void, a stair void, or a space behind a retaining wall works just as well. The search method is the same either way: pick a warm mid morning, stand back, and watch for a repeating flight line. wasps entering and leaving one point in a consistent direction tell you far more than poking around does. When you find that point, mark it from a distance, note the time of heaviest traffic, and keep people away from it until it is treated. Do not put your face near the opening for a better look.
Keeping wasps off a patio without spraying the yard
Most of what keeps wasps circulating through an outdoor space is supplied by the household, and removing it works better than broad spraying. Water comes first here. With about 10 inches of rain a year and humidity near 69 percent, the only reliable moisture in most yards is what irrigation and pools provide. A cracked emitter running every morning, a slow hose bib, a damp pool deck, and towels left over a rail are all consistent sources, and workers memorize them. Food is second, but it is the more visible half. Western yellowjackets scavenge protein and sugar, so open bins, unrinsed recycling, plates left after lunch, and fallen fruit all pay off for a forager. Covered drinks matter more than people expect, since a can left open is a common way to get stung on the lip. The third piece is behavioral. Do not swat at wasps near a table. A crushed wasp releases an alarm pheromone that pulls in more, which is exactly the wrong outcome in a dining area. Move away calmly instead, and deal with the nest separately.
What a good first visit looks like
Expect more looking than spraying. A technician who knows the local pattern will spend the bulk of the visit tracing flight lines, because the opening wasps use is frequently some distance from the comb itself inside a void. They should check the roof to wall junction, attic and foundation vents, tile edges, utility penetrations, stucco cracks, and any slope or retaining wall near the activity. On a property with a pool or heavy irrigation, they should also note the water sources, since those explain foraging that has nothing to do with a nest on your lot. Treatment of a concealed colony is a dust at the entrance after dark, not a general spray of the yard. It is targeted, quiet, and usually knocks activity down within a day or two, though stragglers may return to the entrance for a while afterward. Before they leave, get three answers in writing: whether the comb is being removed and whether that means opening a wall, when the opening will be sealed, and what the plan is if traffic continues past a week. Without a frost to fall back on, the sealing step is what ends the cycle.
How big can a yellowjacket colony really get
It helps to know the outer edge of the range, because it explains why professionals treat hidden nests so carefully. UC IPM's working numbers for California put yellowjacket colonies between 1,500 and 15,000 individuals. That top figure is already several times what most people picture when they imagine a wasp nest. In the warmest parts of the country the ceiling goes higher. Clemson records a huge southern yellowjacket colony found in Charleston County in August 1991, with an estimated 250,000 workers, which is the kind of nest that only develops when mild winters allow a colony to keep running for multiple years. San Diego does not host that species, but it does host the same underlying condition: no reliable freeze to reset the count. The takeaway is not that your wall holds a quarter million wasps. It is that nobody can estimate a concealed colony from the outside, and that a mild coastal winter removes the natural limit other regions rely on. Treat a hidden nest as an unknown quantity, and treat winter activity as a reason to act rather than a curiosity.