Mosquitoes

(Family Culicidae.)

This group includes the familiar insects known as mosquitoes--not a large group, but a very important one, not only from the fact that mosquitoes abound in so many localities and are great annoyances to man and animals, but also from the fact that they are active agents in the transfer of disease. They are found in great abundance in tropical regions, in temperate regions and even far to the North. Travelers in Alaska state that the abundance and voracity of the Alaskan mosquitoes is beyond description. They occur with equal abundance in Lapland and in Greenland.

So far as definitely known the larvae of all mosquitoes are aquatic, although they are true air-breathers; that is to say, they must come to the surface of the water to breathe. They are rapid breeders, and pass the pupal condition also in the water, but floating normally at the surface. They pass through several generations in the course of a year, and hibernate as adults. Hibernating mosquitoes may often be found during the winter months in barns and in the cellars and cold garrets of houses or in sheltered places like outhouses and under bridges and stone culverts. In the extreme southern states many mosquitoes are active all through the winter, and mosquito-bars are almost as necessary at Christmas time as during the summer. Even as far north as Baltimore, mosquitoes sometimes bite in houses in December and January. In places where there are prolonged dry spells, and very heavy rains are only expected at certain seasons of the year, adult mosquitoes live through the dry spells and lay their eggs as soon as the rains come. This is the case in the dry regions of our southwestern country, and it is also the case in tropical countries where the entire year is divided into a wet season and a dry season. In those countries the wet season is generally considered as comparable to our winter, yet it is the active breeding season of mosquitoes, while the dry season, which is supposed to be comparable to our summer, is the season when the adult mosquitoes live on and on. With these insects, as with so many others, the life of the adult seems to be dependent only upon the opportunity of propagating the species. The main purpose of the adult is propagation.

The adult male mosquito does not necessarily take nourishment and the adult female does not necessarily rely upon the blood of the warm-blooded animals. The mouth-parts of the male are so different from those of the female that it is probable that if it feeds at all it obtains its food in quite a different manner from the female. They will sip water or any liquid substance, and appear to be especially fond of beer and wine. The females are normally, without much doubt, plant-feeders, and very few of them get an opportunity to taste the blood of a warm-bodied animal. They will feed upon other than warm-blooded animals. They have been seen puncturing the heads of young fish; they have been seen puncturing the chrysalis of a butterfly, and they have been seen swarming about turtles when the latter are on land. The larvae on the contrary, feed upon all sorts of minute organisms floating in the water, such as the spores of algae and minute aquatic animals. They are all furnished with many bristles at the mouth, and these bristles are kept in constant vibration drawing particles floating or in suspension in the water into the mouth cavity.

Five genera of mosquitoes are represented in this country, namely Anopheles, Aedes, Megarhinus, Psorophora and Culex. Most of our species belong to the genus Culex, and one species of this genus has been selected for the typical life history which is given.

The mosquitoes of the genus Anopheles are the ones which are responsible for the transfer of malaria. The micro-organism of malaria is a protozoon which in the human being inhabits the red-blood corpuscles. It undergoes a sporulating development in the red-blood corpuscles, the spores being thrown into the blood serum afterward entering other blood corpuscles extracting their red coloring matter and destroying them. The full life round of the malarial parasite, however, is not completed until it has been taken with the blood of a human being into the stomach of a mosquito of the genus Anopheles. Here, and here only, is the sexual generation of the parasite developed. Certain of the parasites which undergo no development in the human body, when they are brought into the stomach of the Anopheles continue a sexual development, unite and give birth to elementary forms, known as blasts, which penetrate the stomach wall of the mosquito, enter the salivary glands, and are thus with the poison directed into the body of the next human being punctured by this mosquito.