Diptera

Diptera, the class of insects which includes the Flies. The character of the order is the possession of a pair of clear transparent wings. The hinder wings may be completely aborted, but usually persist as the "halteres" or balancers. The mouth appendages form a proboscis. The metamorphosis is complete, for the larvae are active but footless worm-like maggots. The character of the wings and the rudimentary nature of the posterior pair are the two most prominent characters. The wings are never clad in scales or hairs, and have few veins: most of these are longitudinal. In some cases the number of wings appears to be four, as there is a pair of winglets or "alulae," but these are only lobes of the anterior wings. The two main orders are the Nemocera and Brachycera. The Fleas were once included as a division of the Flies, but are cow generally regarded as a distinct group, the Aphaniptera (q.v.). The principal flies are the House Flies (Muscidce), the Crane Flies (Tipulidce), the Gall Flies and Hessian Flies (Cecidomyidce), the Gad Flies (Sabanidw), the Robber Flies (Asilidce), the Bee Flies (Bombylidee), the Bot Flies: reference should be made to each of these. Fossil flies are rare, except those in amber. The order is a very large one: the British species probably exceed 4,000 in number. The flies are world-wide in distribution, occurring high on the flanks of the Andes and in high latitudes in the Arctic region. In many regions they are a source of serious difficulty, as they attack cattle and horses; some genera cause pestilence, from which man is not free, as in the case of Lucilia, which devastated the French convict settlement at Cayenne. In many parts of the world they occur in such abundance as to form veritable plagues, such as those of the genus Simulium, which have from time immemorial invaded Egypt, and are also met with on the sandy deserts of Western Australia.