CHAPTER XIII 
THE TWO-WINGED FLIES (Order Diptera) 
EXT to the name “bug” there is no other name so 
popular in point of miscellaneous application to insects 
as “fly.” This looseness of popular nomenclature 
may be largely due to the fact that entomologists them¬ 
selves apply the term “fly” in several compound words, 
as butterfly, alder-fly, caddis-fly, May-fly, saw-fly, and 
the like, to widely differing kinds of insects. Used as 
a simple word, however, by fly an entomologist means 
some species of the order Diptera. The various kinds of 
true flies have of course special names, as mosquitoes, 
midges, punkies, gnats, or as in the compounds 
horse-flies, bee-flies, flower-flies, robber-flies, etc. 
The order Diptera is so large and includes insects of such widely differing 
form and habit that it is difficult to formulate any general account of it. The 
name itself is derived from the most conspicuous 
structural condition of flies, namely, their two¬ 
winged state. All Diptera have but a single 
pair of wings, if any; a few are wingless. The 
tiG. 409. Fig. 410. 
Fig. 409.—Mouth-parts of a female mosquito, Culex sp. lep., labrum-epipharynx; md., 
mandible; mx.l., maxillary lobe; mx.p., maxillary palpus; hyp., hypopharynx; li., 
labium; gl., glossa; pg., paraglossa. 
Fig. 410.—Mouth-parts of the house-fly, Musca domestica. lb., labrum; mx.p., maxil¬ 
lary palpi; li., labium; la., labellum. 
hind wings of other forms are replaced by a pair of strange little structures 
301 
