Why Late Summer Is Peak Wasp and Yellow Jacket Season in Southern California

There is a specific stretch of August when the phone starts. Someone was pulling weeds along the side of the garage and got hit four times before they understood what was happening. Someone else has been watching what they assumed were bees drift in and out of a gap under the eave since June, and it is not a drift anymore — it is traffic. Nothing about either property changed. What changed is that the colony living there has been growing since April, and August is the month it finishes growing.

Yellow jackets and paper wasps are annual insects, and that single fact explains almost everything about August. The colony bothering you right now did not move in. It was founded in early spring by one fertilized queen who survived the winter alone — under bark, in a woodpile, in the corner of a shed — and emerged to build a nest roughly the size of a golf ball. She laid the first eggs, hunted the first food, and fed the first larvae herself.

Once that first batch of workers matured, the queen stopped leaving the nest and did nothing but lay eggs. Every worker after that went into expanding the nest and feeding the next generation, and the growth compounds: more workers means more larvae raised, which means more workers. Through May and June the nest is small enough to go completely unnoticed. Through July it doubles, and doubles again. By August it is at or near the largest it will ever be. Then, once cool weather sets in for good, the entire colony dies except for the newly mated queens, who fly off to overwinter alone and start the cycle over next spring.

So the nest in your eave is not a permanent fixture, and it is not there because of anything you did. It is on a schedule. The problem is that its schedule peaks precisely when Southern California is spending the most time outdoors.

Size is only half of it. The other half is a shift in the colony's diet that most homeowners never hear about, and it is the reason wasps that ignored you in June are investigating your plate in August.

For most of the season, worker yellow jackets are hunters. They catch other insects, chew them up, and carry the protein back to feed the larvae. In exchange, the larvae produce a sugary secretion the adult workers feed on. It is a closed loop — the workers get their carbohydrates from the brood they are raising, and they have no particular interest in your kitchen.

Late in the season the queen stops producing worker eggs and the colony turns to raising next year's queens and males. Fewer larvae means far less of that sugary payoff, and thousands of adult workers with nothing feeding them start looking for carbohydrates somewhere else: fallen fruit under the citrus tree, hummingbird feeders, open trash cans, an unattended soda, the bin behind a patio restaurant. This is the point in the year when yellow jackets stop behaving like predators and start behaving like scavengers.

It also makes them harder to shoo off. A wasp working a trash can is not defending a nest, but it is far less inclined to leave when you wave a hand at it — and swatting at one near a nest entrance is how a single wasp becomes several.

If you can point at the nest, you are in the easier version of this problem. Paper wasps build the open, downward-facing, umbrella-shaped combs you see under eaves, inside patio covers, in the corners of door frames, and inside a grill that has not been opened in a few weeks. You can count the cells. You can see the wasps sitting on it.

Yellow jackets are the ones responsible for nearly every multiple-sting incident we get called about, and they usually build where you cannot see them at all. These are the locations worth knowing:

Wasps at a picnic tell you nothing about your property — foragers routinely travel hundreds of yards from the nest. What tells you there is a nest on your property is direction and repetition.

We are not going to tell you every wasp on your property requires a professional. That is not true, and you would know it is not true. Here is the honest line.

A small, new paper wasp nest — golf ball to ping-pong ball size, open comb, well away from doorways, walkways, and play areas, in a household with no sting allergies — is a reasonable thing to handle yourself early in the season, or to simply leave alone. Paper wasps are comparatively docile and are genuinely useful predators in a garden. If it is not in anyone's way, leaving it is a real option, and by late fall it will be empty on its own.

The picture changes when any of the following is true:

One clarification worth making, because it comes up constantly this time of year: we do not service honey bees. A live hive or a swarm is a different trade entirely and not something we take on. But most of the "bees" people find nesting in the ground or inside a wall in Southern California turn out to be yellow jackets, which we do handle. If you are not sure which one you are looking at, describe it to us and we will tell you which call to make.

In most of the country the annual cycle is dependable — sustained freezing weather arrives, the colony dies, done. Southern California does not always cooperate. Our season runs weeks longer than the calendar suggests, and in the mildest coastal pockets a colony occasionally survives the winter rather than dying off. A nest that keeps its queen and keeps growing into a second year can get considerably larger than a normal annual nest.

This is uncommon, not the default, and not something to sit up at night about. It is simply the reason we treat an unusually large nest as a real problem rather than assuming the weather will resolve it, and the reason we would rather deal with a nest in October than tell you to wait for a cold snap that may not come.