No doubt the first step in this direction is a thorough understanding of the creature's life-history. This understanding many able mien are working for. But there is another line of thought that should not be forgotten, though it is negative—many animals are immune. Which are they? Our first business is to list them if we would learn the why of immunity.
Frogs are among the happy ones. One day early in June I took a wood-frog in my hand. The mosquitoes swarmed about. In a few seconds 30 were on my hand digging away; 10 were on my forefinger, 8 on my thumb; between these was the frog, a creature with many resemblances to man—red blood, a smooth, naked, soft skin, etc.—and yet not a mosquito attacked it. Scores had bled my hand before one alighted on the frog, and it leaped off again as though the creature were red hot. The experiment repeated with another frog gave the same result. Why? It can hardly be because the frog is cold-blooded, for many birds also seem, to be immune, and their blood is warmer than man's.
Next, I took a live frog and rubbed it on my hand over an area marked out with lead pencil; at first the place was wet, but in a few seconds dry and rather shiny. I held up my hand till 50 mosquitoes had alighted on it and begun to bore; of these, 4 alighted on the froggy place, 3 at once tumbled off in haste, but one, No. 32, did sting me there. I put my tongue to the frog's back; it was slightly bitter.
I took a black-gilled fungus from a manure pile to-day, rubbed a small area, and held my hand bare till 50 mosquitoes had settled and begun to sting; 7 of these alighted on the fungus juice, but moved off at once, except the last; it stung, but at that time the juice was dry.
Many other creatures, including some birds, enjoy immunity, but I note that mosquitoes did attack a dead crane; also they swarmed onto a widgeon plucked while yet warm, and bored in deep; but I did not see any filling with blood.
There is another kind of immunity that is equally important and obscure. In the summer of 1904, Dr. Clinton L. Bagg, of New York, went to Newfoundland for a fishing trip. The Codroy country was, as usual, plagued with mosquitoes, but as soon as the party crossed into the Garnish River Valley, a land of woods and swamps like the other, the mosquitoes had disappeared. Dr. Bagg spent the month of August there, and found no use for nets, dopes, or other means of fighting winged pests; there were none. What the secret was no one at present knows, but it would be a priceless thing to find.
Now, lest I should do injustice to the Northland that will some day be an empire peopled with white men, let me say that there are three belts of mosquito country the Barren Grounds, where they are worst and endure for 2 1/2 months; the spruce forest, where they are bad and continue for 2 months, and the great arable region of wheat, that takes in Athabaska and Saskatchewan, where the flies are a nuisance for 6 or 7 weeks, but no more so than they were in Ontario, Michigan, Manitoba, and formerly England; and where the cultivation of the land will soon reduce them to insignificance, as it has invariably done in other similar regions. It is quite remarkable in the north-west that such plagues are most numerous in the more remote regions, and they disappear in proportion as the country is opened up and settled.
Finally, it is a relief to know that these mosquitoes convey no disease—even the far-spread malaria is unknown in the region.
Why did I not take a "dope" or "fly repellent," ask many of my friends.
In answer I can only say I have never before been where mosquitoes were bad enough to need one. I had had no experience with fly-dope. I had heard that they are not very effectual, and so did not add one to the outfit. I can say now it was a mistake to leave any means untried. Next time I carry "dope." The following recipe is highly recommended: