Nova Scotia

The downside to a mild fall — a bumper crop of blackflies next spring

A zoologist with the Nova Scotia Museum of Natural History says while we enjoyed a long, mild autumn, it means a "terrific blackfly emergence" come spring.

Unusually mild autumn will likely mean we'll be eaten by blackflies come spring, says Nova Scotia zoologist

Andrew Hebda of the Nova Scotia Museum of Natural History shows a model of a blackfly. (CBC)

With winter in full swing, what exactly happens to those teensy critters that can't warm up by the fireplace?

Dependable weather patterns are essential to insects that are outside all winter, according to Andrew Hebda, zoologist at the Nova Scotia Museum of Natural History.

"They like consistency and they like uniformity," Hebda said. 

Spring pests

In Nova Scotia, blackfly season typically begins in late May running through June. Their bites can cause a number of different reactions in humans, from a small puncture wound to a swelling about the size of a large grape.

Blackflies are biting, swarming pests. (CBC)

Not all blackfly species feed on humans. However, the non-biting species fly around the heads of humans and animals, crawling into the ears, eyes, nose, or mouth, and generally making it miserable to be outdoors.  

Livestock can fall prey to a blackfly species called Simulium arcticum whose saliva contains a toxin which, in large quantities, causes anaphylactic shock and sometimes death in cattle.

Ideal conditions

Hebda said the insects prefer the weather to cool down slowly, with a hard frost to freeze the ground and a layer of snow on top. If there are patterns of thaw and freezing, he said, it messes with their life cycles. 

"If those thaws are prolonged and followed by another cold snap, we'll have fairly substantial mortality, both in insects as well as potentially in amphibians and some of the mammals."

The ideal situation for blackflies is a cap of ice over the frozen ground, keeping the temperature consistent.

Given this year's fine, mild and prolonged autumn in Nova Scotia, Hebda predicts a higher-than-normal population of blackflies next spring.

Fall swarms

In a usual fall, there's a cold snap followed by some warmer weather, bringing out a fresh crop of blackflies.

"In the past, we've had blackfly swarms in November and even beginning of December," Hebda said, "but we didn't get that this year."

Blackflies hatch only once a year, he said, and since they didn't emerge in the fall, there will be even more of them in the spring.

"They're overwintering as pupae, so it means come the spring, we'll have a terrific blackfly emergence," he said. "Something to look forward to."

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