our daily task only by the force of habit; we can neither speak nor think. When the musquitoes disappear, the ‘black-flies’ come: the musquito pumps up a drop of blood and flies away; the black-fly bites and makes a wound which continues to bleed.”
De Saussure has alluded to curious relations which exist in Mexico between a bird, a beast, and an insect. “Bulls bury themselves in the mud,” says this learned traveller, “in order to avoid the attacks of gnats, leaving in the air only the tip of their nostrils, on which a beautiful bird, the Commander, posts himself, in this position the Commander watches for the Maringouin which is bold enough to enter the nostrils of the animal.”
Gnats are parasites in the same manner as leeches, since, like them, they suck the blood, and live at the expense of others. There is, however, this difference, that the females only are greedy of blood; if this fail them, they live, like the males, on the juices of flowers. Another difference is that they are completely harmless till they have wings, and though they live long under their first form, in damp earth or in water, the duration of their life as perfect insects is of short duration.
We need not trouble ourselves about the active larvæ which swarm in stagnant water, nor the chrysalids which float immovable in their natural sepulchre. We give on the next page a representation of a larva of the gnat. The females alone pierce the skin by means of an auger with teeth at the end; they suck the blood, and before they fly away, distil a liquid venom into the wound. This bite seems to have an anæsthetic effect, which does not cause it to be felt till some time after.
The little spot around the wound appears as if affected by chloroform.
Fig. 8.—Gnat (culex pipiens) larva and nymph. (Blanchard).
These parasites repay by an unkind action the assistance which they have demanded from us.
Besides the gnats, which belong to the family of Culicidæ, there are also the Ceratopogon, and especially the Simulium molestum, known in North America under the name of Black-flies: “the tormenting black-flies of this country,” as the Americans say. Certain Nemocera, known by the name of Rhagio, put to flight both man and animals.