MOSQUITOES AND FLIES
thorax, the mouths of which open above the water when the pupa comes in contact with the surface. The pupa, of course, does not feed, but it is almost as active as the larva, for it must avoid its enemies. When disturbed it rapidly swims downward by quick movements of the abdomen, the extremity of which is provided with two large swimming flaps. The duration of the pupal stage in midsummer is about two days.
The adult mosquito issues from the pupal skin through a split in the back of the latter. We now see why the pupa
Fig. 177. Aëdes atropalpus, male, a mosquito related to the yellow fever mosquito and similar to it in appearance
is made lighter than water—it must float at the surface in order to allow the adult to escape into the air.
The full-fledged mosquito (Fig. 174 A) has the general features of any other two-winged fly, but it is distinguished from nearly all other flies by the presence of scales on its wings and on parts of its head, body, and appendages. The mouth parts of the adult mosquito are of the piercing and sucking type, and are similar in structure to those of the horsefly, except that the individual pieces are longer and slenderer, and together constitute a beak, or proboscis, extending forward and downward from the head (Fig. 176 A, Prb). The male and the female mosquitoes are readily distinguishable by the character of the antennae, these organs in the male being large and feathery (Fig. 174 B), while those of the female are
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