Insect guide > Mosquitoes

Mosquitoes


MosquitoesMosquitoes belong to the group Family Culicidae. It's 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 ans 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 specially 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 speculating 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.

We have in the United States three species of mosquitoes of this malarial genus Anopheles, namely A. maculipennis = quadrimaculatus = claviger , A. punctipennis and A. crucians.

The mosquitoes of the genus Aedes are excessively small. Those of Megarhinus and Psorophora are very large, and include the forms known in various parts of the country as gallinippers.

Psorophora is distinguished by possessing upright scales on the legs; Megarhinus by its curved beak. Anopheles is distinguished from Culex by the fact that the palpi of the female are nearly as long as its beak, while in Culex the female palpi are very short.

Mosquitoes as a rule do not fly very far. Those of the genus Anopheles appear to be of extremely short flight. Those of the genus Culex will not fly far away from their breeding places, unless they are carried by light and continued winds.

In heavy winds they cling to the nearest point of attachment. They are carried long distances by airlines, and many localities where mosquitoes were unknown have become infested by the growth of air travel.

Many localities can be practically rid of mosquitoes by the adoption of any one of three measures : either by the drainage or the swamps or ponds in which they breed, or by the use of kerosene upon the surface of the waters in which they breed, or by the introduction of fish into fishless ponds so that they may eat the larvae of the mosquitoes. Read more about mosquito control.

In all mosquito-extermination work, however, it must be remembered that they will breed successfully in any transient pool of water or in any receptacle where water is left standing for a week no matter how small this receptacle may be. They may breed in collections of water in the hollows of old stumps or in old bottles or in old discarded tomato cans. They breed profusely in rainwater barrels, and in rain-water tanks, and in old wells, and even in cess-pools where the adults are able to gain access to such pools. There- fore every possible source of this kind must be hunted for when one is engaged in mosquito extermination.

Life History of a Mosquito
(Culex pungens Wiedemann)
This common and widespread mosquito, which occurs from the White Mountains in New Hampshire to Cuba, and from British Columbia to Mexico, lays its eggs, numbering from 200 to 400 in a raft-like mass on the surface of the water. The eggs are laid side by side, standing on end and stuck close together in longitudinal rows six to thirteen in number and with from three or four to forty eggs in a row-, The egg mass is gray-brown from above and silvery white from below, the latter color being due to the water film. The eggs are laid early in the morning before dawn and in warm weather will hatch by two o'clock on the afternoon of the same day.

The larvae are active little creatures known as wrigglers which are so often to be seen in rain- water barrels and horse troughs. The anal end of the body is provided. with a long respiratory tube into which two large air vessels extend, quite to its tip, where they have a double orifice which is guardeded by four claps. This tube issues from the eighth segment of the abdomen. The ninth segment is armed at the tip with four flaps and six hairs. The flaps are gill-like in appearance, though they are probably simply locomotory in function.

The mouth parts are curiously modified and are provided with long cilia which are kept constantly in vibration, attracting and directing into the mouth minute particles of animal and vegetable matter which are to be found in the water. The 'wriggler remains at the surface of the water when breathing through its respiratory tube but descends when seeking for food. It undergoes three different molts, reaches maturity and transforms to a pupa in a minimum of seven days in hot summer weather taking much longer in the early spring or when the weather grows cool in the fall.

The pupa is well illustrated in the accompanying figure and differs radically from the larva or wriggler from the fact that it now breathes from the ear-like or trumpet-like organs issuing from the thorax instead of from a respiratory tube at the other end of the body. The pupa remains at the surface of the water in an upright position but when disturbed wriggles actively to the bottom, bloating upwards again in a very short time. The pupa stage lasts in warm weather but two days, at the expirationof which time the skin splits on the back of the thorax and the adult mosquito works itself out, resting upon the old pupa skin until its wings unfold, and then tales away. The duration of a single generation may be within ten days ; say sixteen hours for the egg, seven days for the larva and two days for the pupa. This time, however, may be indefinitely extended if the weather be cool.