Why Wasps Get Aggressive in August (And When They Finally Stop)

Wasps get aggressive in late summer because their food source changes. All season, adult wasps feed on a sugary secretion produced by their own larvae. By August the colony has stopped raising workers, the larvae are gone, and the adults are out hunting sugar wherever they can find it — your soda, your grill, your hummingbird feeder. Same wasps, different mission. It ends with the first hard freeze.

They're not angrier. They're unemployed.

This is the part most people don't know, and it explains everything.

For most of the summer, a wasp colony runs on a trade. Adult workers hunt protein — caterpillars, flies, aphids, spiders — and bring it back to feed the larvae. In exchange, the larvae produce a sweet liquid that the adults drink. That exchange is the engine of the colony. The workers are busy, they're focused on hunting insects, and they mostly ignore you.

In late summer, the queen shifts production. Instead of more workers, she starts producing next year's queens and males. The colony stops raising new larvae. And when the larvae are gone, so is the sugar supply that's been feeding every adult in the nest.

So now you've got a colony at its absolute peak population — hundreds of workers, sometimes thousands — with nothing to do and nowhere to get sugar. They go looking. Ripe plums on the ground, open pop cans, garbage cans, the sticky spot on your deck rail, the hummingbird feeder, whatever's on the picnic table.

That's why it feels like they suddenly showed up everywhere and got mean. They didn't change temperament. They changed diet, and their new diet is wherever you happen to be eating.

The timing in Western Montana

Activity ramps up around mid-July, peaks through August, and stays heavy into early September. It fades through late September and ends with the first sustained hard freeze — which around here is usually late September into October, though it swings year to year and comes earlier up the valleys and at elevation.

When that freeze hits, essentially the whole colony dies. The workers, the males, the old queen — all of it. Only the new queens survive, and they don't stay at the nest. They find somewhere sheltered to overwinter — under bark, in a woodpile, in a wall void, sometimes in your attic — and they wait out the winter alone.

Which means the nest that's driving you crazy right now will be empty and dead by November, and it will not be reused next year. Wasps build fresh every spring. If a nest is somewhere out of the way and it's already September, waiting it out is a legitimate option.

Which wasp is it, though?

Not all of them behave the same way, and the sugar-hunting behavior isn't equal across species.

Yellowjackets are the ones at your barbecue. Short, thick, bright yellow and black, and fast. They nest in the ground — old rodent burrows, spaces under stumps and landscape timbers — or inside wall voids and soffits. They're the most aggressive of the bunch and the most likely to sting without much provocation, especially near the nest. A lawnmower going over a ground nest is one of the most common ways people get stung multiple times.

Paper wasps are the long-legged ones with the open, umbrella-shaped nest hanging under your eave or in the porch corner. Legs dangle when they fly. Much more relaxed than yellowjackets — they'll defend the nest if you get right up on it, but they're not the ones raiding your lunch. Honestly, if a paper wasp nest is somewhere you don't walk past, it's doing you a favor by eating caterpillars all summer.

Bald-faced hornets build that big gray papery football you see hanging in a tree or under an eave. Black and white, notably larger. They're not actually hornets — they're a type of yellowjacket — and they are very defensive about the nest. They'll come after you from several feet away. These are not a DIY situation.

What actually helps right now

Since it's a food problem, the fix is a food fix:

• Lids on garbage cans, and rinse the cans out. Sticky residue on the outside of a bin draws them from a long way off.

• Pick up fallen fruit. Rotting plums and apples under a tree are a wasp magnet, and it's usually the single biggest thing in a yard.

• Cover drinks outdoors, and use cups you can see into. A wasp inside a can is how people get stung in the mouth.

• Move the hummingbird feeder away from where you sit, and clean up drips underneath.

• Cover food until you're eating it, and clear plates promptly after.

• Don't swat. A crushed yellowjacket releases an alarm signal that brings others. Stay still or walk away calmly.

And if you're heading out into the woods or working in the yard, watch for a steady stream of wasps going in and out of one spot on the ground. That's a nest entrance, and it's worth marking so nobody mows over it.

When it's not just a nuisance

A nest near a door, a play area, or anywhere kids or pets pass regularly is a different conversation than one in the back corner of a lot. Same with anyone in the house who has a sting allergy, that's not a wait-it-out situation.

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