Only an inscrutable Nature knows why mosquitoes exist. All we can tell you is how. Here’s the criminal record
ONE OF the oldest customs known to man is slapping ladies—lady Culicidae, that is. Mosquitoes to you.
The daddy mosquito rarely gets slapped because, with few exceptions, he doesn’t bite people. When he eats at all he prefers a diet of plant juices and nectar.
Mamma mosquito can get along very nicely on that diet, too, but she’s out for blood whenever she can get it. Nobody seems to know the reason for this blood lust, which makes the mosquito the greatest insect scourge of all time. Even in regions where no animals or people have been for years, female mosquitoes go crazy as soon as one shows up. As far as science has been able to discover, the only effect a meal of hlood has is to make her lay more and bigger eggs.
Mosquitoes belong to the family of insects known as Culicidae or gnats. The name mosquito is a Spanish word, derived from mosca, which means a fly. Entomologists tell us that there are over 120 different genera of mosquitoes and between 1,600 and 2,000 different species. They arc found in every country of the world and in every sort of terrain, including 13,000 feet up in the Himalayas. Most of them live in marshy regions of the tropics where they do inestimable damage by spreading malaria and yellow fever.
In Canada there are about 60 different species of mosquitoes belonging to some eight genera. And besides being a frightful nuisance, they do more real damage than most of us ever imagine. They cost the farmer money by keeping him off the land when he should be getting his spring work done; they bother his cattle and reduce milk production hy as much as 40% in some regions; they have been known to kill newborn calves and foals with their vicious attacks and to worry ewes into leaving their newborn lambs. They cut down on our tourist trade and deprive a lot of people who can’t stand their bites of healthful outdoor recreation.
Mosquitoes spread diseases in Canada, too. The serious epidemic of human encephalitis on the prairies in 1941 was spread by one of our less common species of mosquito, Culex Tarsalis, as was the epidemic of equine encephalomyelitis that killed off so many fine horses. Other species spread bird malaria, which infects domestic and wild birds, and darofilaria, a heart disease of dogs.
And we have malaria mosquitoes. A survey made in 1944 by the Dominion entomology service in co-operation with the medical services of the armed forces revealed that in Canada there are five species of the anopheline mosquil oes, including the dreaded Anopheles Quadrimaculatus, the worst malaria carrier in the United States. Species of mosquitoes capable of carrying malaria were found in every province, but are most plentiful along the Ottawa valley and in southern Ontario.
Although active malaria is not common in this country, one authority on mosquitoes stated definitely that he could see no reason why these
mosquitoes couldn’t spread the malaria brought home from tropical regions by some of our fighting men.
There have evidently been outbreaks of malaria in Canada in the past. John MacTaggert in his book, “Three Years in Canada,” tells of an outbreak of the disease among the workmen who were building the Rideau Canal over a century ago. And in an article entitled “Mosquitoes in Upper Canada,” the Hon. William Renwick Riddell tells of at least two famous men being stricken with malaria, or ague, as it was called in those days— Robert Gourlay and Sir John Ogilvy. The latter died of the disease in 1819.
Fortunately, you can always tell an Anopheles mosquito at a glance. She has a long narrow body and spotted wings, and when she lands on you or on any other surface she sits with her body and hind legs elevated at an angle of about 45 degrees. All other mosquitoes rest with their abdomens parallel to your hide.
But most of our flying hypodermic needles belong to the relatively harmless, if terribly annoying, genus, Aedes. Every region has its own favorite species and they are all stingkers. On the
prairies the biggest pain in the neck is Aedes Campestris, or tennis mosquito, a .medium-sized, frosted-grey rascal that breeds in sloughs. This mosquito is a slightly greater nuisance than the eastern variety because she bites during the hot, sunny days as well as in the evenings.
Another Westerner is a big bully called Aedea Flavescens. She has a body about one quarter of an inch long and is responsible for those tall stories, like the oneabout themosquitoes that ate a farmer’s six-horse team and pitched horseshoes for the harness.
In the central provinces the commonest specieô is Aedes Canadensis, small and dark and mean; she usually bites in the evenings and on dull days. In the northern bush is another big one, Aedes Functor, which drives trappers, prospectors and other northerners almost out of their wits and makes life miserable for all wild life. They have been known along with black flies—to kill caribou.
The Maritimes have a favorite species, too, Aedes Cantator, which breeds in the brackish pools along the coast. Out on the west coast there is another saltwater variety called Aed€>s Taeneorhynchus.
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city mosquitoes and rural mcsquitocr., mosquitoes that like to go indoors and mosquitoes that couldn’t be dragged in. The Culex Pipiens, or rain barrel mosquito, is the commonest city slicker. She breeds in rain barrels, cave troughs, tin cans, old tires or anything else that might hold a few drops of water. She’s the one that buzzes around in your room at night.
All mosquitoes look pretty much alike. They have three main parts to their bodies—head, thorax and abdomen-—two wings and six legs. Different species are different sizes and have different coloring and markings.
But appearance is not always a sure means of identification, since size and color can be affected by the amount of food they get and the color of the water in which they breed. So, if you want to be absolutely certain of calling a mosquito by his right name, here’s what you do. Snip off a tip of the abdomen of a male mosquito—it won’t work with females—about one quarter the size of a head of a pin, boil it in potassium hydroxide to get rid of muscle tissue and examine what’s left under a microscope. The little claspers that you see are different in every species. This, according to entomologists, is the only absolutely sure way of telling mosquitoes apart.
Distinguishing males from females is easier. The males have longer and more feathery antennae.
I)o They Prefer Blondes?
Not all mosquitoes menace human beings. Some just bite animals, others like birds, others only cold-blooded vertebrates such as tree toads, while many species live entirely on plants. There is even one species of mosquito that is nice to have around. These are the Chaoborine of Phantom mosquitoes which in the larva stage feed on the larvae of other more harmful mosquitoes. And when they grow up even the females don’t bite you. In fact they don’t eat at all because their mouth parts are closed up. They live for about 10 days, lay their eggs and just die of hunger. Never kill one of these. You can easily distinguish them because their bodies are completely transparent and, if you look closely enough, you can see all their internal organs.
Whether mosquitoes prefer blondes or brunettes or redheads has always been a startling question. Experiments carried on with Aedes mosquitoes by the U.S. Armyduring the wardisproved the old notion that mosquitoes have any color preference. An arm bathed in red light was attacked by ravenous females as readily as one bathed in green light. They were slightly repelled by black or white clothing, preferring the intermediate shades. Green seems to be their favorite color.
But, as a matter of fact, mosquitoes don’t see so well anyway and rely more upon their senses of feel, smell and hearing, which are all located in the antennae. A mosquito with eyes removed found her victims quite easily but not so one who had lost her antennae.
Be careful always to get down wind from mosquitoes, because the U. S. Army tests showed that they are attracted by air that has blown past a human being. They can feel warmth for quite a distance and prefer warm sweaty skin to cool dry skin. St) you are more likely to be bitten if you are working hard around the yard than if you’re just sitting in the shade having a tall cool one. A nice thing to know.
What kind of skin do mosquitoes
love to munch? Well, the tests showed that they definitely prefer soft tender skin to a tough hairy hide. Which would seem to indicate that they prefer humans to animals and women to men. Fair enough, considering it’s the women mosquitoes that do the biting.
Some people react more violently to mosquito bites than do others, but nobody seems to know just why. Some entertain the theory that a vitamin B deficiency might be the cause while others say that we build up an immunity to mosquito bites and the more we are bitten the less the bites will affect us. They point to the fact that persons from countries where mosquitoes are scarce, little babies and city folk swell up worse than farmers and others who are exposed to mosquitoes regularly. If this theory is right then the only way to become immune is to sit around and let mosquitoes bite you. The cure might be worse than the disease.
They Don’t Really Bite
But actually, in the proper sense of the word, the mosquito doesn’t bite at all. She sucks your blood. That long beak of hers—or proboscis, to give it its proper name—is really a prolongation of the lower lip. It is made up of six different parts including a hollow tube and tiny drills and saws all covered by a protective sheath.
The proboscis is connected with the salivary glands and as soon as she jabs you the mosquito shoots a little saliva into the hole to prevent the blood from clotting. This juice acts as an irritant and causes the bumps and makes you scratch. Too much of it can make your lymph glands swell up and put you in bed for a few days. If you don’t scare the mosquito off before she is finished she may draw the irritant back, but don’t bank on it.
There are several commercial treatments for mosquito bites, but a little daub of iodine is as good as anything. Northerners often use strong cold tea, since the tannic acid has a curative effect as it has on burns.
Taken all around, the mosquito is perhaps the worst insect enemy that man has ever had. They have retarded the development of whole continents, such as Africa; they have decided the outcomes of wars by killing more soldiers than the enemies’ weapons. In the opinion of some historians they were more responsible than the Goths and Vandals for the downfall of ancient Greece and Rome.
For the Anopheles and Stegomyia mosquitoes are entirely responsible for the spread of malaria and yellow fever, respectively. Other mosquitoes spread denyou fever and blackwater fever. But mosquitoes do more than just spread the diseases, as flies spread typhoid, for example; they are the intermediate hosts to the parasites that cause the diseases. This means that the parasites go through part of thendevelopment within the body of the mosquito and without the mosquito there never would have been any malaria or yellow fever.
It Is frightening to think of the attempts that were made to combat these diseases before Ross and Grassi and Reed discovered who the real villains w-ere. Almost everything except mosquitoes was blamed for the spread of the plagues. Suspected clothing was burned, ships’ cargoes pitched into the sea, thousands of stricken persons left to die on quarantined ships. During the first hopeless attempt to build the Panama Canal, when malaria and yellowfever were killing thousands of workers daily, doctors, in an attempt to protect
patients from bothersome insects, actually placed the feet of hospital beds in pans of water. And in these pans the mosquitoes that were spreading the diseases bred in the millions.
During the last war the American Army, before attempting a landing on any South Pacific island, first drenched it from the air with DDT to kill a foe far more deadly than the Japanese.
Life of a Mosquito
All mosquitoes require water, salt or fresh, to complete their life cycle. They cannot breed in long wet grass as some people believe.
The reason there are so many mosquitoes around in early spring is that the Aedes female lays her eggs in the late summer or fall and they hatch first thing in the spring. One mosquito will lay several hundred eggs which she deposits in low, wet places. In the spring these low places become temporary pools and the eggs float on the surface of the water where they are hatched by the heat of the sun.
Not all mosquitoes do it this way, though. Other less common genera such as the Anopheles, Culex and Theo baldía have more than one generation a year and winter in the adult stage. That big mosquito you see around first thing in the spring is a fertile female that has hibernated in a cellar or a hollow tree or some other likely spot. She is full of eggs and is ready to drop them wherever she can find a little water. It doesn’t take much. The female of one species lays her eggs in the few drops that collect in the bowl of the pitcher plant.
When the eggs hatch the water is full of little wrigglers that look like tiny twigs about one eighth of an inch long. These larvae feed continually on decaying organic matter and on minute forms of animal and vegetable life known as plankton. The wrigglers are eaten in turn by minnows, beetle larvae and damsel fly nymphs. Each wriggler has a little tube on its rear end which it sticks up out of the water every so often to take in air. It is while doing this that the mosquito is most vulnerable. A little oil on the surface of the water will plug the tube and kill the larva.
The length of time the mosquito remains in the larva stage depends on the temperature of the water and the amount of food. When full grown it changes into the pupa stage. The pupa, which looks like a top-heavy comma, doesn’t eat anything at all, but just moves about in the water in a sort of stupid end-over-end fashion that has earned it its nickname, the tumbler. The pupa also has a special air tube or “trumpet” which it sticks out of the water every so often.
Then one day the pupa goes to the surface of the water and cracks open. The adult gingerly crawls out, all set up with wings, proboscis and everything else needed to set herself up in the business of being a nuisance. She has to float around on the pupal case for a few minutes until her wings dry. If the weather gets too rough she may fall off and drown—and nobody cares. That is one reason that mosquitoes don’t breed so well in large bodies of water such as lakes or in rapid flowing streams or rivers.
Tests have shown that for about a day after emerging from the pupa the female mosquito is content with plant juices and is not interested in blood. After that she can’t get enough of it.
The male mosquito doesn’t eat much of anything. He just hangs around for three or four days and then dies, with or without having performed his biological function. The life span of the female depends upon the alertness of
the people she bites and her own ability to escape the bats, birds, and dragon flies that prey upon her in flight. With luck she may be around for a month or six weeks and, of course, some species live through the winter.
It would be nice to think that the female goes off somewhere and dies after filling up on blood, but it ain’t so.
Like all insects, mosquitoes are more active in warm weather than in cold. Generally speaking the prairie and coastal mosquitoes bite during the day, while the bush mosquitoes bite during the evenings.
Most mosquitoes stick pretty close to their home pool, but occasionally they do get a yen to travel. Scientists have found this out by having the adult pass through a special dye as it emerges from the pupal case. When it is killed and dipped in alcohol it turns a brilliant purple. Some of these tagged mosquitoes have been found over a hundred miles from their birthplaces.
That annoying hum that drives you nuts in your bedroom at night and causes campers to knock over tent poles waving at something they can’t see is made by the female mosquito. She has a little gimmick at the base of her wings that produces the hum when she flaps them. The faster she flaps the higher the pitch.
This hum is really a mating call. It attracts the male mosquitoes who hear it through their delicate antennae. When you see a swarm of mosquitoes above your head in the evening, flying around in a circle and going up and down in a sort of dancing motion you don’t need to worry about them swooping down and strafing you. They are male mosquitoes just waiting around for thegirls to come out. When a female goes humming by, a number of males detach themselves from the swarm and race after her. Unlike drone bees, the male mosquito does notdie immediately after mating.
Male mosquitoes can be attracted by a tuning fork vibrating at between 350 and 750 vibrations per second. This fact has led to the building of elaborate traps designed to eliminate the race by attracting male mosquitoes into a screen and doing them in with electricity.
A much cheaper and better means of eliminating mosquitoes is to destroy their breeding places by getting rid of any little deposits of water that may be sitting around. A dirty yard is a mosquito hatchery. Keeping grass and weeds cut down also discourages mosquitoes from making your home theirs.
Drainage of swamps and sloughs is, of course, an effective means of mos-
quito control. But there is always the danger of upsetting the balance of nature by destroying the natural breeding places of insect-eating birds. It also must be remembered that mosquitoes in fish-bearing bodies of water are a part of the natural food chain from plankton to larvae to small fish to larger fish. The fewer mosquito larvae the fewer minnows and the fewer game fish.
Placing oil on the surface of bodies of water that harbor mosquitoes is another widely used control measure. The Dominion entomologists suggest a medium grade of petroleum oil to which has been added a small amount of 25% tar acid ( } ■> gallon to every 100 gallons of oil), but ordinary kerosene works just fine, too.
DDT kills mosquitoes as it does all insects. It may be sprayed on the walls of animal and poultry quarters or on the inside of tents. Airplanes have spread it over large areas with good results. A one per cent DDT water suspension or aqueous emulsion sprayed around the yard on vegetation in which mosquitoes hide gets rid of a lot of them without injuring the plants.
DDT, however, will not protect animals or humans from mosquito bites because mosquitoes are not repelled by it. While doing experimental work in the bush, investigators whose arms were covered with a 35% solution of DDT found mosquitoes burrowing through the stuff to get at their skin.
However there are some excellent repellents available. During the war much experimental work was done on mosquito-bite prevention and a number of good solutions were developed. The old stand-bys such as citronella, oil of lavender, spirits of camphor, oil of tar are out of date; they gave protection up to an hour and a half. The new mixtures containing such chemicals as 2-ethyl-l, dimethyl phthalate, hexanednoil or indolene give immunity for up to five hours.
In some parts of Canada municipal governments have taken steps to control mosquitoes. Winnipeg and Ottawa are perhaps the l)est examples. For 15 years Ottawa has been spending $7,500 annually on mosquito control in an area around the capital covering about 50 square miles. Results have been excellent. In other places service clubs have undertaken the work. The Young Men’s Section of the Board of Trade in Saskatoon, Sask., for example, holds tag days to raise money for equipment and labor for this work.
But in spite of all these efforts the mosquito population continues to thrive and we continue to slap ladies. ★