Which wasps you actually run into around Los Angeles
Five social species cover nearly everything here, and they split cleanly into two groups by risk. The yellowjackets are the serious ones. UC IPM identifies the western yellowjacket as the most commonly encountered species in Los Angeles, the one people call a meat bee for the way it works over grilled food and pet bowls. It nests out of sight, in soil cavities and structural voids. The German yellowjacket is the newer worry in town. UC IPM describes it as becoming more common in urban areas of California and frequently nesting in houses, which turns a yard problem into a building problem. Its colonies live in wall voids and attics where the comb is invisible and the population is unknown until someone opens the wall. On the mild side, native paper wasps and the European paper wasp build open combs of 15 to 200 individuals, per UC IPM, and they mostly sting when their comb is touched. Bald-faced hornets, the enclosed gray nest builders, are less common in the basin but do turn up in trees and under wide overhangs, and they defend a much wider circle.
Why some colonies here never die off
In most of the country the wasp season has a hard stop. Frost kills workers and the old queen, and the nest is finished. Los Angeles does not get that reset. The average winter low sits near 48 degrees, and UC IPM states that in very mild winters or in coastal California south of San Francisco, some yellowjacket colonies survive for several years and become quite large. That single fact changes several decisions. A nest you were planning to wait out may not go quiet in December. A colony entering its second year begins the season with a standing workforce rather than one queen, so it reaches dangerous size months earlier. And a wall cavity that housed a multi year colony can hold a large amount of accumulated paper and debris. Practically, this means you should not assume an old nest is empty, and you should not postpone a wall or attic nest into winter hoping the weather handles it. Watch the entrance for traffic on a warm afternoon. If wasps are still moving in January, treat it as an active colony and get it inspected rather than waiting for a season change that may not arrive.
When a wasp nest counts as an emergency
Most nests can wait a few days for a scheduled appointment. A few cannot, and the difference is about people, not about the wasps. Treat it as urgent when someone in the household has had a serious reaction to a sting before. The American College of Allergy, Asthma and Immunology reports a 60 percent chance of a similar or worse reaction after a prior allergic sting reaction, which removes any argument for waiting or for handling it yourself. Treat it as urgent when the entrance sits within a step or two of a door, a gate latch, a stairway, a mailbox, or a pool ladder. Those are places people reach without looking. The same goes for a nest at a child's height near a play structure or a sandbox. Treat it as urgent if wasps are appearing inside the house. That means the colony has found a route through a wall or ceiling, and the count only rises. Meanwhile, keep everyone away from the area, do not spray at wasps flying near the entrance, and do not crush them, since a crushed wasp releases an alarm signal that pulls in more.
What the first visit looks like at a Los Angeles home
Expect the inspection to take longer than the treatment. A technician who does this well will spend most of the visit watching flight lines, because the hole wasps use is frequently some distance from where the comb actually hangs inside a void. They will check attic vents, the roof to wall junction, weep openings, utility penetrations, and any gap in the eave. The treatment itself for a hidden colony is usually a dust placed at the entry, done at dusk or after dark when nearly all workers are inside. It is quiet, targeted, and does not involve saturating the yard. Activity typically drops sharply within a day or two, though you may see stragglers returning to the entrance for a while. Ask three questions before they leave. First, is the comb going to be removed, and does that require opening a wall or ceiling. Second, will the opening be sealed, and when. Third, what happens if traffic continues past a week. In a climate without a killing frost, the sealing step is the one that decides whether you are doing this again next year.
Keeping wasps off a patio through a dry summer
Prevention here is mostly about water and food, in that order. With roughly 15 inches of rain a year and humidity around 71 percent along the coast, wasps spend real effort finding moisture. A slow drip at a hose bib, a cracked drip emitter, a pet bowl topped up in the morning, or the wet edge of a pool deck all read as a water source, and foragers will keep returning to it. Food is the second half. Western yellowjackets scavenge both protein and sugar, so an uncovered trash bin, a plate left after lunch, a recycling bin holding rinse free cans, or fallen fruit under a citrus tree all keep wasps circulating through the yard. The structural half of prevention happens in late winter. Walk the patio cover, eave line, pipe ends, umbrella poles, and grill lid in February and March, when a queen is working alone on a comb the size of a coin. Knocking one down then takes seconds. Screening attic and foundation vents at the same time closes the routes that lead to the wall void nests nobody wants to find in August.