Why do wasps sting in autumn?

Wasps tend to be at their most irritating in October – but why? The answer, it turns out, lies in the of the insects' anatomy and ecology

10th August 2018

Summers can be glorious, full of lazy days in the garden, sunny afternoons in the pub  and ice creams on the seafront. But as they start to wane, the relaxing hum of bees visiting flowers turns into a persistent buzz of wasps.

Wasps have been around all year, so why is it that they only become so irritating now?

wasp on food
In late summer and autumn, wasps have a habit is spoiling picnics ©Getty
Wasp ecology and anatomy

The answer actually lies in the unusual ecology and bizarre anatomy of social wasps. In the spring, queen wasps wake from hibernation and start to build their nest, laying eggs and raising their first brood of daughters. These worker wasps cannot produce fertilised eggs so spend their time helping their mother expand the nest and raise more young.

One of their main jobs is searching for soft bodied invertebrates to feed the developing larvae. Bizarrely, adult wasps cannot digest the food they catch because their gut is so constricted by their thin "wasp waists". Instead the workers chew up the prey and feed it to the larvae. In return the larvae produce a sugar rich spit that the workers can drink.

common wasp
Adult wasps cannot digest the food they catch because their constricted gut ©Getty
Intoxication leads to irritation

The colony will go on expanding throughout the summer until the queen decides to produce males and new queens. After these "reproductives" have left the nest, the old queen stops laying. This means the workers no longer have access to larvae. Instead they live on the sugar produced by rotting fruit and tree sap. This can be a problem because fermenting fruit contains alcohol so wasps can become intoxicated and rather irritating. 

They are also attracted to the abundance of sweet foods that humans provide. To a starving wasp a jam sandwich or a can of coke is just too tempting to avoid. For this reason, wasps are generally only a nuisance in late summer/autumn; the rest of the year they are too busy hunting, expanding the nest and defending it. Remember that these drunken workers don’t have long to live - as soon as the winter weather sets in the entire colony will die, leaving only the queens to hibernate through to the next year.

Jess Price works for Sussex Wildlife Trust.

Main photo ©Getty

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