The part played by certain blood-sucking Diptera in the dissemination of disease is now well known (see Mosquito and Tsetse-Fly), and under the term myiasis medical literature includes a lengthy recital of instances of the presence of Dipterous larvae in various parts of the living human body, and the injuries caused thereby.
The dipterous gall-formers include the gall-midges, or gallgnats (Cecidomyidae), minute slender-bodied insects, with bodies usually covered with long hairs, and the wings folded over the back.
In animals galls occur mostly on or under the skin of living mammals and birds, and are produced by Acaridea, and by dipterous insects of the genus Oestrus.
Typical dipterous insects (flies) closely resemble in general form aculeate Hymenoptera belonging to the families of bees and wasps.
The best-known dipterous pests are the Hessian fly (Cecidosnyia destructor), the pear midge (Diplosis pyrivora), the fruit flies (Tephritis Tyroni of Queensland and Halterophora capitata or the Mediterranean fruit fly), the onion fly (Phorbia cepetorum), and numerous corn pests, such as the gout fly (Chloropstaeniopus) and the frit fly (Oscinis frit).
The dipterous garden pests, such as the onion fly, carrot fly and celery fly, can best be kept in check by the use of paraffin emulsions and the treatment of the soil with gas-lime after the crop is lifted.