Wasps: The Scourge of Autumn

By Elaine Farragher

I remember a particularly stunning day last autumn. Clear blue skies, cool, invigorating temperatures, gorgeous fall colours. The perfect day to set off for a stroll in the park and a picnic lunch on a bench.

However, I had forgotten one important factor, one which I seem to forget every year until I am again rudely reminded. The pesky yellow jacket wasps.

At this time of year everyone experiences the persistent and threatening harassment of these bright yellow and black insects, who, attracted by any available meat or fruit, drive us outdoor diners indoors in droves, wondering why we ever attempted “dining out” in the first place. For “isn’t it the same every year?”

Yes it is, and it might even be getting a little worse, as the main culprit, the German yellow jacket, a European import, makes greater inroads into the North American scene. The European variety is more aggressive, more likely to nest in populated urban areas, and remains active longer in autumn than our native species.

For most of the summer yellow jackets of both varieties are not nuisances at all but quite beneficial to humans since their diet is largely insects. So what turns them into nuisances in the fall? To understand this we have to take a look at their life history. Except for the queen this extends only from spring to fall.

In spring the queen, who has overwintered in some sheltered crevice, crawls out at the first real warmth and starts a period of rather frantic activity. Our native species of wasp usually chooses an underground mouse burrow or cavity underneath a rock to begin her colony. More rarely, she hangs her nest from a tree. The European variety picks a crevice in a wall or attic of a building. Both species chew up wood pulp and mix it with their saliva to produce a gray paper which they ingeniously fashion into six or eight eight-sided cells, with the opening facing downwards. These cells are protected by a paper umbrella which will later be extended to produce a totally enclosed balloon-shaped nest with an entrance near one end.

The first eggs that are laid in these cells by the queen become, in about a month’s time, sterile adult females that take over the nest building and feeding of the young. The queen can now relax and begin to perform her chief function: laying eggs in the new cells which are being built by her rapidly multiplying offspring. As more and more wasps mature and get to work producing more wasps, the colony has a population explosion. In a successful colony, a nest which started with the efforts of one queen will by late summer number between two and five thousand wasps.

As the nest grows, layers of paper from inside the nest are removed to make way for more cells, re-chewed, and added to the outside of the nest. Underground burrows are enlarged by dumping the soil outside.

Finally, by midsummer, the queen lays two kinds of eggs, fertile males and females, which are the only sexual brood of the summer and the last eggs the queen will lay. When these mature and leave the nest to do their mating, the worker wasps are suddenly left with nothing to do. Not only that, late summer brings a decline in the insects which are their main source of food, just at the time when their own numbers are at their absolute peak. To feed themselves, they spend more time away from the nest, becoming the thieving, dangerous nuisances so familiar to our autumn days. Fruit and meat become their main food and picnickers are handy food distributors.

The males and fertile females do not bother us; they are too busy mating. And since the sting is a modified egg-laying apparatus, the males don’t have one anyway. The sterile female workers, however, certainly have them and seem ready to use them. Unlike the honey bee, they do not leave their stinger behind after they have stung, but can use it repeatedly. During the summer months the wasps sting only in defense of the nest. But their fall idleness makes them aggressive and unpredictable and much more likely to use their stingers.

The yellow jacket wasps are effective insect predators in the summer months, and are instrumental in controlling many garden pests. So destroying wasp nests can have some undesirable side effects. However, when a nest is in our house, it should be dealt with, preferably by a professional if the nest has already grown to its mid-summer size. Some people are dangerously sensitive to the stingers’ venom, although most of us will only get a mildly sore lump.

But the fall problems can be curtailed if we are careful with our garbage and if we are aware, when we pack our autumn lunches, that we will have some uninvited guests if we have open food containers to attract them.

Elaine Farragher, September 1988

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