DIPTERA.
All suctorial insects which in the perfect state possess only two membranous wings, are called Diptera, from two Greek words—δις, twice, and πτερον, wing.
The Diptera were known and scientifically described at a very early date. They are frequently mentioned by Aristotle in his "History of Animals;" and he applied the term to the same insects as now constitute the order.
The absence of the second wings, common to other insects, which are in this case replaced by two appendages, which have received the name of balancers, [10] because they serve to regulate the action of flight, constitutes the chief characteristic of the Diptera. Let us, however, give a glance at their other organs, which have more or less affinity with those which exist in other classes of insects, preserving, nevertheless, their own especial characteristics.
The mouth, for instance—suited for suction only—is in the form of a trunk, and is composed of a sheath, a sucker, and two palpi. The antennæ are generally composed of only three joints. The eyes—usually two in number—are very large, and sometimes take up nearly the whole of the head. They are both simple and compound. The wings are membranous, delicate, and veined; the limbs long and slight. In giving the history of the principal types of Diptera, we shall explain more fully the formation of these organs.
The Diptera, by their rapid flight, enliven both the earth and the air. The different species abound in every climate, and in every situation, some inhabiting woods, plains, fields, or banks of rivers; others preferring our houses. They like the neighbourhood of vegetation, choosing either the flowers, the leaves, or the stems of the trees of our woods, our gardens, or our plantations. Their food varies very much; and the formation of the sucker is regulated by it. Some imbibe blood, others live on the secretions of animals. Their chief nourishment, however, consists of the juices of flowers, on whose brilliant corollas the Diptera abound, either plundering from every species indiscriminately, or attaching themselves to some particular kind. They display the most wonderful instinct in their maternal care, and employ the most varied and ingenious precautions to preserve their progeny.
The Diptera, besides their variety and the number of their species, are remarkable on account of their profusion. The myriads of flies which rise from our meadows, which fly in crowds around our plants, and around every organised substance from which life has departed, some of which even infest living animals, are Diptera.