Will we ever control the BLOODTHIRSTY BLACK FLY?


Will we ever control the BLOODTHIRSTY BLACK FLY?


Will we ever control the BLOODTHIRSTY BLACK FLY?


At this moment black flies are rising by the billion from rivers and streams across Canada. In desperate self-defense holidaymakers are struggling into heavy protective clothing, daubing themselves with sticky repellents, and doing their best to enjoy themselves in a haze of insect-killing sprays. In spite of their precautions the black fly is going to ruin thousands of carefully planned vacations. Its vicious bite will drive people indoors at noon, and its numbers will sometimes make it hard for people to speak — or even breathe.

The black fly is thickest in the north, where, with its biting colleague the mosquito, it has been an often-overlooked factor in retarding economic development. It breeds and bites just when work in the north is reaching its brief and crucial summer climax. It attacks pulpwood workers, trappers, construction men, soldiers, airmen and radar operators, and cuts their efficiency when it's needed most.

The black fly is equipped with serrated jaws that cut like saws. By slashing these cutters together, he literally chops a hole in you. A pool of blood forms in the hole, and the black fly begins drinking.

Sheer numbers of hungry black flies have sent men rushing panic-stricken through the bush in search of refuge. Black flies have killed cattle, grouse, ducks, turkeys and caribou. They've sickened thousands of holidaymakers with the after effects of their bites.

Contrary to common belief, the black fly is not an exclusively Canadian pest. Its close relatives—they look and behave just like the local variety—infest the whole world. They kill cattle in Europe, blind natives in Africa, disrupt work in Central America and infuriate Russians, Chinese and Australians.

While we slap and curse the black fly wâth as much futility as anybody else, Canada is perhaps the first nation to control the pest even partially. This control, achieved within recent years by the combined efforts of the Defense Research Board, the Department of Agriculture, and the Pulp and Paper Association, has nearly eliminated black flies in some places. But for most people the black fly is as much of a problem today as it ever w'as.

On its own, the black fly isn’t particularly fearsome. Its bite isn’t as painful as that of a gnat so small it’s called no-see-um. It doesn’t take as much of your blood as a mosquito, it bites only

It kills cattle, ruins vacations and disrupts work in the woods. Even with DDT we can't wipe it out completely— and some scientists say we’ll wreck one of nature’s cycles if we keep trying

w'hcn the humidity is between seventy and ninety and the wind is light, and it sleeps all night. Of the sixty varieties that live in Canada, only a couple—Simulium venustum Say and Prosimulium hirtipes (Fries) — are major biters of mankind. What makes the black fly extraordinary is its numbers; it wall infest areas to a point where outdoor human activities practically come to a standstill.

The black fly is a tiny insect, about an eighth of an inch long, with short broad wings and short legs. On your arm. it looks like a small black gnat. When one lands on you it scuttles rapidly into biting position, preferably in a dark place —under your watch strap, under your belt, in

your socks, or maybe under your hat brim. Seen through a microscope it has a peculiarly determined look, with a permanently humped back as though it was hunching its shoulders forward over its low-slung head.

The species begins life as a tiny glistening yellowish egg, laid under or near fast-flowing w'ater. It hatches into larva within a few days or else spends the entire fall and winter as an egg. Each fly lays between three hundred and a thousand eggs, and the total number of eggs laid by a colony of flies can stagger the imagination. A member of the Federation of Ontario Naturalists last summer estimated at sixteen million the number of black fly eggs he saw on a fifteen-foot-long

rock outcrop near a waterfall in Quebec Province.

After developing in larva form, the black fly spins a cocoon (or pupa) underwater. Later it bursts from the cocoon as a fully grown fly, ascends to the surface in a bubble of gas, and immediately takes off. The adult fly may live several days or several weeks. Some subspecies live through a single generation, and others as many as four generations between April and October. In the far north the cycle lasts only from the end of June to September.

The black fly’s function in nature is obscure. Some birds eat it on the wing and its eggs and larvae provide food for other insects and some varieties of fish. Many people claim its true func-

tion is to harry, infuriate and bite every available Canadian. A diamond driller, C. P. Barager, at work in muskeg country in Ontario, once claimed he needed a flashlight to see his way through clouds of black flies in daylight. In 1891 a Harvard scientist, A. S. Packard, was horrified at the numbers of black flies in Labrador. He reported they were so thick they sent Newfoundland dogs howling into the water to lie partially submerged out of the black flies’ reach.

Till 1947, Canadians endured attacks of similar virulence with hapless resignation. But then the Defense Research Board, alarmed by the way black flies could shatter the fighting spirit of soldiers in the north, asked the Department of Agri-

culture to investigate methods of combating the menace.

Soon after this Dr. Bryan Hocking (University of Alberta), Dr. C. R. Twinn (Department of Agriculture), and W. C. McDuffie (U. S. Department of Agriculture), found through intensive experiments at Churchill, Manitoba, that one part of DDT mixed with ten million parts of water killed black fly larvae in rivers and streams, but left everything else unharmed.

This was the beginning of a battle against the black fly during which the insect was studied as intensively as a neurotic on a psychiatrist’s couch. Scientists wanted to know every mannerism of the black fly so they could continued on page 63

Will we ever control the bloodthirsty black fly? continued from page 31

One dedicated scientist sat on a rock and let swarms of flies bite his bare stomach

strike it down where and when it was weakest.

A team of entomologists made thousands of black flies radioactive and then pursued them with Geiger counters, trying to determine their range. One scientist, Dr. Douglas Davies, now teaching at McMaster University, sat on a rock in Algonquin Park with a square inch of his stomach exposed and let a swarm of black flies bite him. He found out how many landed in a minute and how many bit under a wide range of conditions, even checking on which colors attracted and repelled the insects. His work confirmed a bush belief that dark clothing attracts black flies. He also found that lighter colored clothing tends to repel them.

Scientists working on control agreed that the best protective uniform was loose-fitting, light-colored clothing tied tightly at the neck, waist, wrists and ankles, with a hat with repellent-soaked strings hanging from it. Repellents, long scorned by bush workers, were improved during the northern black fly battle. One new repellent, to be put on the market soon, is reputed to maintain its effectiveness in clothes for more than a year despite washings.

Curiously, although there are dozens of repellents on the market few of them have common chemical ingredients. Nobody knows why they repel black flies, except that the insect doesn't seem to like the smell of them.

“Once we have more specific knowledge about the odors the black fly likes and dislikes."’ says Dr. A. S. West, a black fly expert at Queen’s University, “we'll be able to develop much more effective repellents.”

Hitten loggers leap for lakes

The same trial and error approach that is being used in the search for repellents sets a limit on the pace of progress in control measures. Once it became generally known that DDT was sudden death to black fly larvae, enthusiastic farmers and country property owners—seizing their first chance to be rid of the accursed fly—often overdosed streams and rivers with DDT.

One man who owned a stream in northern Ontario was told by D. G. Peterson, a leading Department of Agriculture entomologist, that he would need two tablespoons of DDT to clear out the black fly larvae in the two-feet-wide trickle. “We discovered later,” says Peterson, “that he dumped forty-five gallons of DDT into the stream.” The poison killed every living thing for miles downstream.

By 1952 the black fly fighters could control the pest in limited areas, mainly because the range of the insect is short —about five miles. But more widespread control seemed to be too expensive and difficult to be practical. At that stage the Canadian Pulp and Paper Association entered the fight. Localized control wasn’t good enough for the pulp and paper operators. Foraging parties of woodcutters might range for miles through the bush. On these forays the men were being bitten so badly that some jumped into streams and lakes to escape. Hundreds of men were refusing to go into the bush at all during the fly season.

In 1954 two DDT-spraying airplanes ranged across a twenty-six-thousandacre tract of timber land located at Baie Comeau, on Quebec’s north shore, one of the pulp and paper industry’s worst black fly areas. When the last

of the reports from the Department of Agriculture and pulp and paper entomologists was in, it seemed that at last the harried workers in the basin could take a deep breath without inhaling black flies.

Billions of adult flies and larvae died in the attack, and although other black flies immigrated into the area later there was comparative peace at Baie Comeau for weeks. That’s where black fly control stands today. "More widespread

control, to give relief to holidaymakers right across Canada,” says Dr. West, “may never become a fact.”

Scientists studying the black fly have spent much time analyzing the effects of the insect’s bite, but they admit they still don’t know too much about it. Black fly bites hurt some people intensely, but they hardly affect others. Some people achieve immunity against the bites —this is specially true of Indians—but others remain perpetually sensitive.

Dr. Douglas Davies of McMaster University has noticed that late-season bites are often worse than early season bites. He has watched black flies feeding on his hand under a microscope, and he’s seen them pumping with their bodies as they drank, as though pushing saliva into the incision. He has noticed that a kind of salivary sac near the stomach has apparently been pumped empty as the stomach.filled with blood. Dr. Davies theorizes that perhaps the sac contains an anesthetic coagulent which is full and effective at the beginning of the season but becomes exhausted after many bitings.

When people are first bitten they may have little reaction. But these first bites seem to sensitize their victims. Later bites cause slight swelling, reddening and itching, and in some more serious instances, swollen glands, fever and nausea.

D. G. Peterson, of the Department of Agriculture, says that once a person has been sensitized a delayed reaction causes “the formation of an itching weeping papule that irritates for a week, and perhaps as long as a month.” Bites also infect the lymph glands and cause “black fly stiff neck.”

In fighting to control the black fly scientists found that the physiological effects

of bites may be serious, and if there are enough of them they can kill a man. But it is the psychological effects of black fly bites that do the most damage. There is no immunity against this. Dr. Bryan Hocking, of the University of Alberta, has reported that repeated bites, along with the noise of the pests and the sensation of flies hitting the skin in thousands, soon produces an illusion that the insects are biting even when the last of them is gone.

He says that under intense attack many men become “ineffective” from mental stress far sooner than from physical causes. “The rapidity with which a susceptible person can become worked up into an emotional state bordering on dementia . . . has to be seen to be believed,” says Hocking.

Looking for an opening

A former woods-survey crewman of Toronto, Ken Wells, says he doesn’t know of anything more morale-shattering than feeling thousands of black flies hitting your hands and face and hearing them pattering against your clothing. “You watch your friends at work clearing brush,” he says, “and you see millions of black flies scuttling over their clothing, hunting desperately for an opening. It’s no wonder that some men want to run away.”

One of the most unpleasant effects of black fly bites is the seepage of blood from the bite. This is caused by the black fly’s technique of cutting a hole in you, rather than inserting a tube and drinking like most insects. Children attacked by flies frequently present a frightening appearance, the backs of their heads ringed with a line of clotted blood. Black flies bite children along the

hairline, presumably because that's the first dark spot they find after they land.

A well-known Toronto angler, Dr. Arthur James, recalls canoeing for the first time in northern Ontario before World War I, and suddenly seeing the back of his brother's head streaming with blood. “1 found it hard to believe that a few buzzing gnats could have done that,” he says. He knows better today. Last summer he ran into a swarm of black flies so thick he couldn’t breathe. He had to flee from his fishing ground.

Human beings have been able to escape the black fly by enduring the acute physical discomfort of heavy enveloping clothing and by smearing repellents and spraying DDT. But cattle were never >o lucky. Before the northern control campaign against black flies started in 1947, one of the worst black fly areas in Canada was along the banks of the North and South Saskatchewan rivers. In spring and summer black flies sporadically burst from these rivers in fantastic numbers and mercilessly harried cattle on nearby farms. Six hundred cattle died in 1940, the worst year; thousands had died there in black fly attacks in the past 50 years or so.

Nobody knows precisely why so many black flies infested that particular region, although both rivers have many fast-flowing, shallow stretches — ideal black fly breeding grounds. Until more modern methods of control came into use, farmers set smudge fires to give off choking smoke, and built dark shelters of brush and branches into which cattle could retreat. The smudge fires were sometimes effective, but too often dead cattle were found lying in the hot embers of the fires after frantic efforts to escape the biting demons all around (hem.

In Africa a bite can blind

How the black fly kills cattle is a mystery. Some entomologists say it is death by shock, caused by millions of tiny punctures. Others believe the poison in the bite causes a breakdown in the lymph glands. It* is known that animals can suffocate through sucking thousands of the insects into their lungs during bad attacks.

But Saskatchewan’s problem, which the Department of Agriculture is solving today by dumping drums of DDT off a couple of bridges crossing the two rivers, was never as bad as Europe's. In 1934 eleven thousand cattle died in Yugoslavia in black fly attacks, and Rumania suffered the worst black fly plague of all time in 1923 when sixteen thousand domestic animals died as clouds of flies rose from the Danube River.

Canadians are lucky, too, in that local varieties of black fly don’t carry diseases harmful to man. On the Gold Coast of Africa, now part of the state of Ghana, called “the country of the blind,” fifty thousand natives are sightless from a disease—onchocerciasis—carried by a species of black fly almost identical in appearance and habits to the Canadian breed. Thousands of natives suffer from the same disease in Central America.

Another black fly disease ruins cattle


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hides in some parts of the world, but fortunately misses Canada. However, Canadian entomologists are uncovering evidence that may prove much of the damage done by the black fly is hidden far beneath the surface of the struggle for survival in the insect world.

Dr. A. M. Fallis, of the Ontario Research Foundation has said that black flies have killed domestic ducks by infecting them with a malaria-like blood disease but little is known about their effect on wild-duck population. In the U. S. turkeys and other fowl have

died from this disease, and Canadian grouse go through peculiar slumps and surges of population which may be caused by the same disease.

In fact, some entomologists believe that black flies may have an important effect on many species of wild birds. Complete elimination of the black fly, even if it were possible, might be undesirable. It is possible that the destruction of such a numerous insect could disturb one of the balances of nature.

At any rate the control victories against the black fly in Canada, although

spectacular, are still limited. Complete control is still a dream for a holidaymaker with a hundred of the insects crawling down the back of his neck. Dr. Bryan blocking of Alberta once said that the best counter measure for the average person to adopt against the black fly was “the cultivation of an attitude of patient tolerance.”

He added. “It is certain that despite airplanes and DDT, and anything that these may immediately foreshadow, the biting fly will he a feature of life in the north for many years to come.” ★