Mosquitoes or gnats (Culicidce) belong to the order of insects known as Diptera. As is well-known, a typical member of the class Insecta has four wings, but it is characteristic of members of the order Diptera that the hinder pair of wings are so reduced in size as to form only small knobs called ” balancers ” or halter es, so that Diptera are often spoken of as ” two- winged flies.” Other important characteristics of members of this order are that they possess piercing and sucking mouth parts, and that they undergo complete ” metamorphosis ” a term which is ex- plained by Glaus in the following manner :
The more complete the agreement between the just-born young and the adult sexual animal so much the greater will be the duration of the embryonic development and the more complicated the developmental processes of the embryo. The post-embryonic development will, in this case, be confined to simple processes of growth. When, however, the embryo is born in an immature condition and at a relatively low state of organization, the post-embryonic development will be more complicated, and the young animal, in addition to its increase in size, will present various processes oftransformation and change of form. In such cases the just-hatched young, as opposed to the adult animal, is called a Larva and develops gradually to the form of the adult sexual animal. The development of larvas, however, is by no means direct and uniform, but is compli- cated by the necessity for special contrivances to enable them to procure food and to protect themselves ; sometimes taking place in an entirely different medium, under different conditions of life. This kind of post-embryonic development is known as metamorphosis.”
The phenomena of metamorphosis are exceedingly well shown in the life history of frogs and in that of most insects. The different stages through which mosquitoes pass before they reach the adult state may, for example, be briefly described in the following way:
The adult mosquito lays its eggs on the surface of water. The eggs float on the water for some days (two to four), after which
time they hatch and permit of the escape of the larva.
The larva is a free swimming, worm-like animal, which eats greedily and grows rapidly, casting its skin several times in the process, till it reaches its full development. At this stage it suddenly changes its form ; casting its skin, the worm -like larva assumes a comma shape, and so becomes the pupa or nympha.
During the pupal period the insect ceases to eat ; profound anatomical changes take place within the pupal skin, whereby the masticatory mouthparts of the larva are converted into the suctorial apparatus of the adult insect or imago. After a certain number of days the pupa-case ruptures, and the adult insect is liberated, furnished with wings and legs adapted for a life in the air.
The Diptera have been divided into two great groups, termed Orthorrhapha and ^yclorrhapha, according to the manner in which
the pupa-case splits to permit of the escape of the perfect insect. In the Orthorrhapha, which includes the Culicidoe (mosquitoes), the ChironomidcB (midges), the Simulidce (sand-flies’, the Cecidomyidce (gall-midges), the Mycetophilidce (fungus-midges), the Tipulidce (daddy-long-legs), the TabanidcB (horse-flies), etc., the pupa-case splits longitudinally down the median dorsal line. In the Cyclor- rhapha, which includes the Syrphidce (hoverflies), the Oestridce (bot-and warble flies), the Muscidce (houfee flies, tsetse flies, blue and green bottle flies, flesh flies, etc.), the perfect insect escapes by the splitting off of a cap from the head end of the pupa.
The members of some of the above families are not infrequently mistaken for mosquitoes, especially the ChironomidcB or midges, the Cecidomyidce or gall-midges, the Tipulidce, the Simulidce, and the Psychodidce or owl-midges. Mosquitoes may, however, be easily distinguished from any other flies by the following characters :
- They possess a long sucking proboscis.*
- The veins on their wings are covered with scales.
- The arrangement of their wing-veins is characteristic and different from that of the members of any other family.
Resource – A Monograph of the Anopheles Mosquitoes of India By William Glen Liston, Sydney Price James