A new study by researchers at Trent University has shown that sedentary behaviour benefits wild mammals by significantly reducing the harassment from biting insects.

“Biting insects, like deer flies, have manifold effects on mammal hosts,” said Dr. David Beresford, professor of Biology and in the Trent School of the Environment. “Through this study, we uncovered an effective behavioural counterstrategy by large mammals to these persistent biting flies, and our experiment was elegant in its simplicity.”

Biting flies are serious pests for humans and other large mammals. Blood-seeking insects, such as deer flies, often cause distress to wild mammals, leading them to alter their behaviour. Caribou in the boreal forest, for example, appear to reduce activity when deer flies are numerous. However, as a means to reduce insect harassment, such sedentary behaviour seems counterintuitive, perhaps even counter-productive.

Professor Beresford alongside Trent Biology professor Dr. James Schaefer and undergraduate student April DeJong reasoned that a moving host might attract more deer flies because of continual exposure to new deer flies. In contrast, a stationary host should attract only nearby deer flies; few new flies should arrive once nearby flies are deterred by the host or are satiated with a blood meal. For the host, inconspicuousness should be advantageous.

A simple experiment leads to surprising results

The study, which was published in the latest issue of the Canadian Journal of Zoology, details a simple experiment, where April conducted field trials during warm summer days, serving as the potential host to deer flies. Each day, for 20 minutes, she either walked along a forest trail or she sat quietly along the trail. To determine fly abundance, she wore a hat with a sticky tape on the back; each minute she counted the number of deer flies on the trap. To test their hypothesis, the team compared the accumulation of deer flies, minute by minute, walking versus sitting.

The paper offers stark results: while walking, the human host attracted 5 times as many flies per minute compared to sitting. While the host was sitting, deer flies rapidly declined to almost zero by 20 minutes. In contrast, while the host was walking, this decline was much more gradual, never reaching zero. This outcome provides evidence that sedentary behaviour can benefit large mammals by lessening their conspicuousness to deer flies.

“This was an experiment unlike any other I’d done,” said April, now a Trent alumna. “I realized that controlled studies are not restricted to the lab. Ecologists can carry out carefully designed studies in the real world.”

Biting insects have gained appreciation for their role in the evolution and ecology of large mammals. This experimental study adds to understanding how potential hosts might respond to deer flies.

Learn more about Trent University’s Biology program.