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Crane Flies — Part 2

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 railroad trains, and many localities where mosquitoes were unknown have become infested by the introduction of railways or improvement of the through train service.

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. 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 rain-water 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. Therefore 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 rainwater 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 guarded by four flaps. 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 locomotary 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, floating upwards again in a very short time. The pupa stage lasts in warm weather but two days, at the expiration of 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 flies 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.