The distribution of the Culicidce is practically "world wide." From the tropics to the polar regions they are encountered, and in such desolate regions as the tundras of Siberia they occur in countless myriads. It is probable that these Culicidce of cold regions do not belong to the subfamily Anophelince, and, on the contrary, it is probably true that the Anophelince are especially numerous in the tropic regions of the earth.
Migratory nights of Culicidce have been described, but they are a rare phenomenon, and during the last few years that particular attention has been directed to them, no similar occurrence has been noted. These flights were observed in Victoria, Texas, U. S. A. They occurred after a strong easterly wind had been blowing for some days, when a cloud of mosquitos flying about 50 feet above the ground appeared. The "flight" was about three miles wide and lasted for about five days, following the course of the wind. The flight probably originated in a marsh 35 miles away. A second similar flight occurred seven years later. The flight was about 10 feet above the ground and extended to a distance of about 60 miles. Such a phenomenon is undoubtedly exceptional, and, as we shall see, there is good reason to believe that, under ordinary circumstances, the normal flight of mosquitos is very limited,-to be measured in yards rather than miles,-and that mosquitos have a distinct aversion to wind. Our own experience has often confirmed this point. On the west coast of Africa, when a stiff land breeze was blowing, one could sit in one's bungalow free from the attacks of Stegomyia, and if a tornado was raging, there was no sign of mosquito life.
On the other hand, in addition to migratory flights, there is. a certain amount of evidence to show that mosquitos may fly as far as 20 miles if a steady wind sets in a particular direction, mosquitos having been encountered out at sea that distance from land; but, in my opinion, most of these statements require to be received with caution, as it is not at all improbable that the source of the mosquitos lies in some overlooked place on board, in some uncovered water butt or some recently opened hold.
That mosquitos travel in railway trains may daily be observed in the tropics, but that the few introduced into a locality in this way could be the cause of their appearing where previously absent is exceedingly doubtful. Many of the older statements about mosquitos must be received with great caution, as it requires an expert to detect all possible breeding places, and a statement by a nonexpert that mosquitos are absent from a place must be examined very carefully. That mosquitos have ever been introduced by ships or railways from one continent to another there is no evidence to show, and, in fact, the well defined areas of distribution of the Anophelince are against this. Certainly it would be an interesting experiment to make, e. g., the transportation of an Indian anopheles to
Africa, and vice versa. We shall consider some of these points more in detail when we come to the Anophelince.