The mosquitoes (culicidae) are a family of two-winged insects with long "beaks," and the instinct (in the female) for sucking blood. There are many different genera, or kinds, of mosquitoes, but the only ones which are of practical importance around New York are the two kinds called respectively culex and anopheles. These can be easily distinguished from each other. Of the culex variety we are concerned with two sub-varieties: Culex pipiens, which develops in fresh water, and culex sollicitans, which grows in salt water. Mosquitoes have four stages of development; the egg, the larva, the pupa and the winged insect. They propagate only in water. The eggs are very small, oval, black objects not so large as a fly speck. In the case of culex they are mostly stuck together side by side in little flat brown masses, each mass containing several hundred eggs. The eggs are set on end in the masses. In anopheles they are only lightly adherent, and lie flat, end to end. The eggs are laid on water, upon which they float, or in mud. The end of the egg, after 36 or 48 hours (or more, in cool weather) opens, and the larva escapes. Under very favorable climatic conditions, the larvae may appear in 18 hours. The larva of culex is the familiar "wriggler" of pools and water barrels. A larva of culex is drawn in Fig. 2. It will be noticed that the insect in this stage hangs downward, only its breathing tube or wind-pipe connecting with the surface of the water. When disturbed, it dives and can remain without air for half an hour or more, though it usually rises to the surface again in about half a minute. After the lapse of from one to three weeks (according to the temperature of the water), when it has grown to be about one-quarter of an inch long, the larva splits its skin and the pupa (which corresponds to the chrysalis stage of the butterfly) appears. The pupa is drawn in Fig. 3. It has two wind-pipes instead of one, and these are located near the head instead of at the tail-end. It flaps its tail violently and sinks to the bottom of the water when disturbed. After from one to four days in warm weather the pupa in turn bursts its skin up the back, and the adult insect appears, with wings, ready soon to fly, and in the case of the female to bite and lay more eggs. The complete female culex is drawn in Fig. 3. The "beak," it will be seen, has a long middle piece (proboscis) and two smaller projections at each side of the proboscis, which Fig. 2.-Larva of Culex at Surface of Water, and More Highly Magnified. are called feeders or palps. These palps are very short in the female; but in the male culex they are longer than the proboscis and very hairy. Just outside the palps are two long antennae, each with fourteen small joints; the antennae are much more feathery in the male than in the female. This mosquito is the familiar pets of fields, gardens, woods and houses everywhere. Only the female bites. In warm weather she can digest a meal of blood in 36 hours or less. The culex mosquito selects, to deposit her eggs, only still or slowly flowing water, but not even the most advanced degree of putrescence or contamination prevents the eggs from developing; thus cess-pools, brewery drains, and stable yard pools are favorite spots. One species develops with great rapidity in salt marshes. Eggs are usually laid in water barrels, pans, tin cans, wells, springs, rain-pools, cess-pools, pots, kettles, drainage traps, ponds, marshes, holes in hollow trees-in short, anywhere where stagnant water remains in warm weather for a week or two at a time. The young (larvae) of culex pipiens will be found in almost any standing water; while those of anopheles may be found only in clean, shallow, shady and grassy pools. The first can be at once recognized as not being anopheles larvae by their position, hanging head downwards. If one leans over a pool containing anopheles larvae and waits a little he will be able to see them lying horizontally on the surface of the water. He must wait a little, however, as they are apt to dive when one approaches them; also they frequently run to the edge and hide in the grass, so they are sometimes not so easy to find even when present. The best way to get them is with a white dipper. Dipping in the water unless you see larvae is not the best way; make a quick strike, just skimming the water towards the edges of the pool. Carry it into the grass, because the larvae are in the grass. Do not make this stroke until you have given the larvae time enough after you arrived to dive and to return to the top. Another way is to press the edge of the dipper suddenly under water, so that the stream of water running into it may wash the larvae into the dipper. The young anopheles are light grey, banded with black, and very slender. The older ones are red, green, black, etc., the color depending on what they eat. They are less slender. All are quick in movement, and although they will dive, yet they also dart along the surface of the water, which the others never do. Some are extremely small. Culex sollicitans, or the salt marsh mosquito, is a migratory insect. It voluntarily leaves its home, and will be found many miles from its breeding place. This variety represents 80 per cent. of the mosquitoes found in New York City. Anopheles, which is the mosquito that under certain conditions causes malaria, is not the common species of this region, but still is present in many localities. It differs from culex as follows: The larva swims flat on the water Fig. 4. Resting Posture of Mosquitoes; 1 and 2 Anopheles; 3 Culex pipiens. (After Sambon.) instead of head down, and has a very short breathing tube. The adults, both male and female, have their palps or feelers just as long as the proboscis instead of much shorter, or much longer; and the wings of all the species found in this vicinity are spotted (see lower part of Fig. 4). These differences can be easily MS. made out with the naked eye. Another point of distinction is that when anopheles is at rest on a wall it sits with its body almost at a right angle; while culex holds its body parallel with the surface it rests on (Fig. 4). Anopheles Fig. 5-Adult Female Culex. prefers to deposit its eggs in pools of rain water on the ground, but will breed almost anywhere else, when such pools are lacking. Añopheles flies chiefly at night. Fig. 6-Wing of Culex (above) and of Anopheles (below). Ms. SURFACE OF WATER K The Life Progression of a Mosquito: A-The Eggs Cluster. B to C-The Hatching of the Larva or Wriggler. C-The Larva with Its Breathing Tubes in Contact with Air. D-The Terminal By Courtesy of United States Drainage & Irrigation Co. |