Deer flies, horse flies having 'good year' in Ottawa due to rain

If you've noticed an abundance of pesky deer flies and horse flies buzzing by — and leaving you with painful bites along the way — it's no surprise given the wet summer so far in Ottawa.

Fly researcher Jeff Skevington says blood-sucking flies thrive in wetness

A federal research scientist says intermittent rain has fueled the population or larger insects. 1:54

If you've noticed an abundance of pesky deer flies and horse flies buzzing by — and leaving you with painful bites along the way — it's no surprise given the wet summer so far in Ottawa.

Deer flies, along with the typically larger horse flies that are part of the same Tabanidae family, thrive in mucky soil and water, according to Jeff Skevington, a fly researcher at Agriculture and Agri-Food Canada.

"There seems to be more than usual this year," he said, adding that he is not aware of a quantitative study on the numbers this year compared to previous years.

"On a dry year, the muck along pond edges dry out, the ponds recede, then its horse flies and deer flies dry up. This year, we've had intermittent rain through the season, so it's a good year for them."

Bites always come from the female flies, who need the blood to nourish their eggs, while the male flies feed on flowers, Skevington said.

"When you're being bitten by them, you're probably close to a lake or a pond  — somewhere where the larvae are in abundance," he said.

Bug spray won't work

Your first instinct might be to grab for bug repellant but Skevington warns that won't work with deer flies and horse flies.

If you look closely, you'll notice Tabanidae flies have large eyes, which guide them to their prey, unlike mosquitoes, whose heat and carbon dioxide sensors are disrupted by repellant.

Skevington recommended wearing whites and tans to avoid being seen by the flies — or standing next to a tall person.

"They're always around the tall person. You'll find that they always go to the higher places," he said. "They're going to be mostly around your head so wearing a hat will stop most of the biting."

He added the wet summer could also lead to more mosquitoes, which breed in water.

"The more you refresh the temporary pools that the mosquitoes are breeding in, you get more mosquitoes, and with horse flies and deer flies, the more mucky their pond margins, the more larvae will survive." 


To encourage thoughtful and respectful conversations, first and last names will appear with each submission to CBC/Radio-Canada's online communities (except in children and youth-oriented communities). Pseudonyms will no longer be permitted.

By submitting a comment, you accept that CBC has the right to reproduce and publish that comment in whole or in part, in any manner CBC chooses. Please note that CBC does not endorse the opinions expressed in comments. Comments on this story are moderated according to our Submission Guidelines. Comments are welcome while open. We reserve the right to close comments at any time.