Nature_reflections_06-20

Jeff Green | May 18, 2006

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Black flies

by Jean Griffin

"Blackfly, little blackfly, always a blackfly, no matter where I go. They'll find the blackfly pickin' my bones, in north Ontar-io-io, in north Ontar-iooo" - not only in Northern, but also Southern, and in fact, right across Canada! - and beyond.

Does it help to learn that in Canada there are over 150 different species of these little pests? No? Then maybe it will help to learn that only very few of these species are those that attack humans. Each species is very selective as to their choice of host, and many feed only on the blood of birds. Also there are some kinds that apparently do not have blood-sucking mouthparts and do not take blood at all. Those that do, tend to attack in swarms, often making outdoor activity without protection disagreeable.

Black Flies are small, from one to five mm in length, rather squat, with large, rounded wings and a humpbacked shape. Most common in spring and early summer, it is, like the mosquitoes, the females that bite. Often landing and taking off repeatedly without biting, the buzzing presence and crawling is almost as irritating as the biting. As sundown approaches the numbers seem to increase, but once darkness arrives the pests disappear, as they do not attack at night. Unlike mosquitoes, they seldom attack indoors or in an automobile, as their attention seems to be diverted to finding an escape route, so they crawl up and down screens or window panes.

After mating the female Black Flies usually lay their eggs on the water where they gradually sink. Hatching in a matter of days, the larvae will produce silk pads securely attached to rocks, and then attach themselves to these home bases with abdominal hooks. One biologist describes the larvae that you might see (if you care to look) as "small black twiglike objects about a quarter of an inch long" attached to a rock and looking more like plants than insects. Here though bent downstream by the force of any current, they filter the water for food.

Try brushing one of these larvae off its silken base and it starts to rush downstream, but suddenly stops even in swift water, and then starts to move back upstream. What has happened? When dislodged, the larva immediately spins a silken thread, one end of which is attached to the silk pad. Once out of ‘harm’s way’, it stops, grasps the thread in its mouth and by eating the strand of silk ‘reels’ itself back to its home base, where it resumes feeding. Amazing!

The larval stage is replaced underwater by the pupa, safe in a small cocoon, still with two feathery gills to extract oxygen from the water while it changes to the adult. Once metamorphosis is complete, the pupal case splits open and the adult in a tiny bubble of air rises to the surface where the bubble bursts and the adult is ejected into the air and flies away. And so "Blackfly, little blackfly, always a blackfly, no matter where I go"!

Observations: White-crowned Sparrows were seen on May 5 by Sandra Moase in Sharbot Lake , and on May 9 by Helm in Oconto. Barbara Geddes, Sharbot Lake , saw a Scarlet Tanager on May 9. Also on the 9th, Markus Saunders and Shirley Peruniak saw two Eastern Milk Snakes in the Clarendon area. Fred Johnston saw an American Woodcock on Fall River Road on May 8. Many thanks to all who phoned in their first sightings of the hummingbirds! Share your observations, call Jean at 268-2518 or email This email address is being protected from spambots. You need JavaScript enabled to view it..