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24 Aug 2021

Wasps – a picnic ruined

Written by Roddy Hamilton, Ranger in our North-East region
A familiar sight for those out and about in late summer: the wasp
Wasps: the uninvited guest at every summer picnic, and seemingly always bad-tempered. But why? Trust ranger Roddy reveals that the key to understanding wasps’ behaviour lies in their very complicated – and rather incredible – life cycle.

It’s a quintessential late summer scene at Crathes Castle: families and friends are gathered on the lawn just downhill from the castle, on tartan picnic rugs strewn with crusty bread and cheddar cheese slices, peeled tangerines and jam scones. There can be heard the chatter of nearby children, the occasional rustle of the newspaper page being turned, and the soft effervescence of a fizzy drink.

Then, all in a moment, the idyll is shattered. The newspaper is rolled up and begins furiously swiping the air. Wasp!

Why do wasps appear determined to ruin our picnics? And why does it always seem to be later in the year?

One of our favourite summer pastimes, a picnic in the sun

It’s to do with the wasps’ very complicated and rather incredible life cycle.

In the early spring, the queen wasp emerges from her winter hibernation to form a nest in which to lay her eggs. You might recognise her by her size – much bigger than the more usually-seen worker wasp.

You may also hear her. Sitting in my own garden, I can often hear the strong mandibles (an insect mouthpart; paired jaws) of wasps ‘chewing’ wood from my garden table. This the queen will use to create a paper pulp with which to build a nest. A wasp nest is an architectural marvel, created as it is from a cluster of cells. In each of these cells she will lay an egg.

Through the summer the queen will lay eggs to become worker wasps, who will then tend all of the queen’s offspring. The offspring, or larvae, in the cells will be fed insects hunted by the worker wasps. In return, the larvae will secrete a sugary substance to reward the worker. All the time this is happening, the queen is releasing pheromones, or chemical messages, which instruct the workers. And this is key.

The inside of a wasp nest. Wasps crawl in and out of the hexagonal cells crafted from paper-pulp.
The expertly crafted paper-pulp cells of a wasp nest

These pheromones, as well as the sugary rewards given to the workers, unite the colony. At this point wasps are not a problem to us. In fact, they are very much a benefit to us and the ecosystem in general: they are consumers of large amounts of insects so keep numbers of plant pests down, and they also pollinate our wildflowers and garden blooms.

Unfortunately, as the summer wanes and the temperature cools, the queen stops laying worker eggs. She now lays only eggs that will become males and new queens, which will mate and then hibernate to start the cycle all over again next spring.

The queen dies, her job done. And with her departure goes the pheromone instructions which united the colony. There are also very few larvae left in the cells of the wasp nest, and so the workers – receiving no instruction from the queen and no sugary reward from the larvae – go on a marauding, confused quest for sugar. This of course leads them right to our picnics.

Wasps are drawn to our sugar-filled picnics, lured in by fresh fruit and our sweet fizzy drinks

These invasions are what gives wasps a bad name. And of course the fact they can sting. Swiping a newspaper at a marauding wasp, however, is unlikely to be the best course of action. You may kill the wasp, but you run a greater risk of being stung yourself as it sees you as a threat.

Compared to bumble bees, wasps’ public image is undeniably poor. They can’t compete in the cuddly charts with our buzzy bee friends; their smooth bodies appeal to us less than the bees’ furry bodies. But how fair is it that we impose our human judgment so readily, given the ecological benefits they provide the environment?

Taxonomically, wasps and bees share a common ancestor. Scientists believe that at some point bees made the decision to become vegetarian, and decided to get all their food requirements from flowering plants, while wasps followed the carnivorous route. This might also be a part of their image problem. But it’s difficult to look at a wasps’ nest and its architectural ingenuity, or to imagine their complex social life cycle, without feeling at least a little admiration.

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