TORONTO - With more seasonal temperatures expected to arrive this weekend, campers, cottagers and anyone else heading into the wilderness in Canada's eastern half are being warned about a proliferation of a common summer menace: blackflies.
Weather conditions through the winter and spring have been ideal for unleashing the puny pests, particularly across the Canadian Shield, where the insects seem to do particularly well, experts say.
"We're probably in for a good year -- if you like blackflies," said Doug Currie, an insect expert and professor at the University of Toronto.
Heavy snowfall over much of eastern Canada last winter, along with high water levels during the spring, have resulted in the perfect environment for breeding more blackflies than usual, Currie said.
"It's all tied to the availability of habitat."
The nasty little biters usually begin to appear around this time of year and typically peak in mid-June, petering off around the end of the month.
It's a similar story in New Brunswick, which saw near-record snowfall last winter that helped to insulate the eggs through the cold season, then provided lots of fast-running water for larvae to grow in the spring.
"There's been lots of water this spring and that means we'll likely get lots of bugs," said Stephen Heard, a biologist at the University of New Brunswick.
"For the blackflies, that means more streams running and the ones that are running are bigger so there's more room for the larvae."
Christian Back, vice-president of science and research with GDG Environnement, a Quebec-based insect-control company, said technicians observed larvae density three to five times higher than usual in rivers and streams from Labrador to southern Ontario.
"That's a very significant and measurable increase," Back said.
A blackfly's average lifespan is around three weeks, he added. How many of the critters last into the later summer months depends on the weather.
Environment Canada issued a long-range summer forecast Wednesday, predicting this summer would be hotter than usual after a cool spring.
In and around Toronto and southern Ontario, temperatures are expected to climb to a high of 32 C over the weekend, though forecasts for much of the rest of Canada aren't quite so sweltering.
Canada is home to more than 100 species of blackflies, which grow to a maximum length of about a centimetre. They are most abundant in wooded areas, as far north as the Arctic.
Eggs are laid in running water, and the species remains there until it becomes an adult fly. It floats to the surface fully able to fly and, in the case of females, bite.
Blackflies feed on the blood of animals and people, and love crawling into clothing to lodge themselves in nooks of the body for a feeding frenzy - they bite repeatedly. Blackfly bites leave a small, bloody spot behind that is often intensely itchy.
Bites have been known to cause headaches, nausea and swelling of the lymph nodes, but severe reactions are rare. Blackflies aren't known to carry any diseases that affect humans in Canada, though in parts of Africa and South and Central America, they carry pathogens that cause serious illness.
The flies can spell serious problems for livestock. Many bites will cause animals to lose weight and fail to thrive. There have also been instances of cattle dying of anaphylactic shock -- a serious type of allergic reaction -- after multiple blackfly bites.
QuickTips: strategies to avoid getting bitten by blackflies this weekend
- Avoid being outside during times of day when blackfly attacks are most severe - morning, late afternoon and early evening.
- Wear light-coloured clothing, to which blackflies are less attracted.
- Tuck pant legs into socks or boots and wear snug, long-sleeved shirts - blackflies often crawl into warm regions such as the armpits to feed.
- Bring a mosquito net to wear over your head when going into areas where blackflies are thicker, such as heavily wooded areas and near running water.
- Insect repellent containing DEET is effective; natural products such as citronella also work but may need to be re-applied more frequently.
