Why are wasps so aggressive in August?
By Wespenprofis.ch · Reviewed by:Fachbewilligung Schädlingsbekämpfung VFB-S · Updated: 3 July 2026
At a glance
In August and September a wasp colony reaches both its maximum size and its most aggressive phase. Food becomes scarcer, more workers are defending the nest, and if a colony loses its queen (a queenless colony), the remaining workers react particularly badly to any disturbance.
Peak colony strength falls in late summer
A wasp colony grows steadily throughout the summer, but only in August and September does it reach its maximum size, with the greatest number of workers in and around the nest at the same time — several thousand insects in the case of larger colonies. The more insects there are defending a nest, the more likely encounters with people become — and the more coordinated the defensive response to a disturbance. The guide Wespensaison Schweiz sets out how this fits into the year as a whole.
Less food, more competition
In early summer, workers mainly collect insects to supply the brood with protein. From late summer onwards, hardly any new larvae hatch, demand for protein falls, while the workers’ own need for sugar rises. Ripe fruit, open drinks and sweet food outdoors therefore become the main target — and draw considerably more insects to one spot than in June, which further reinforces the impression of increased aggression.
When a colony loses its queen
Colonies whose queen dies in late summer react especially badly. Without the regulating influence of the queen, the “queenless” colony loses its balance: the workers lose their division of labour and defend the nest far more aggressively than usual, sometimes with no recognisable outside trigger. To an outsider, such a colony is barely distinguishable from a normal one — which is why caution near a nest is generally advisable in late summer, whatever the state of the colony.
How to behave around a nest
Move calmly and without sudden movements near a nest, cover food and drinks outdoors, and stay clear of the area directly in front of the entrance hole. At night the entire colony remains gathered inside the nest, as the guide Wespen bei Nacht und Regen describes. This peak phase lasts only a few weeks; the guide Wann sterben Wespen im Herbst describes what happens afterwards. If a nest is active in an awkward location, removal should be left to a professional — details at /wespennest-entfernen.
Frequently asked questions
Why do wasps become more aggressive in late summer?
The colony is at peak strength, natural food outdoors becomes scarcer and sweet foods attract more insects — all of which raises the likelihood of encounters and defensive reactions.
What does a "queenless" colony mean?
A colony that loses its queen in late summer. Without a queen the workers become increasingly unsettled and react extremely badly to any approach towards the nest.
Does the behaviour change again in autumn?
Yes. With the first cool nights the colony collapses, and the aggression drops away quickly as the workers die off.