DIPTERA 815 



attention of cl>e young student. But the larvas of many species cause 

 the growth of galls on plants, some of which are sure to be found by 

 any close observer. Other species arrest the 

 growth of the plants they infest, and cause very 

 serious injury. 



The larv^se are small maggots, with nine pairs 

 of spiracles. The head is small, poorly developed, 

 and without mandibles; between the head and the 

 first thoracic segment there is a large neck-seg- Fig- 1034. Head 

 ment, which gives these larvae the appearance of ?Jg th^SlasT- 

 having an extra segment. Many species are bone, 

 brightly colored, being red, pink, yellow, or 

 orange, and many species possess in the last larval instar a peculiar 

 chitinous organ on the ventral aspect of the prothorax; this organ is 

 known as the breast-bone or sternal spatula, or anchor process (Fig. 

 1034). It varies in form in different species; different views are held 

 regarding its function, none of which seems well established. 



The lar\'al mouth-parts are fitted only for taking liquid food; but 

 the nature of this food differs greatly in different members of the 

 family. Some species are parasitic in the bodies of aphids and other 

 Homoptera; some are predacious feeding on either aphids, coccids, 

 mites, or ISiTvse. and pupse of other Diptera, especially those of other 

 species of gall-gnats; some feed on the excrement of other larvag or 

 that of cattle and of birds; but most species are vegetable feeders. 

 Among those that feed on plants many species produce galls. The 

 larvffi of several genera of the second subfamily, the Heteropezinse 

 give birth to living young, as described later. 



Different modes of pupation have been observed among the gall- 

 gnats ; in some the pupa is naked ; in others the change to the pupa 

 state takes place within a puparium, but this puparium differs from 

 that of most Diptera in being formed by the next to the last larval 

 skin, the last larval molt taking place within it ; in some species as the 

 wheat-midge, the pupariiim consists only of the peunltimate larval 

 skin, in others as the Hessian fly, it is lined with a delicate silken 

 Isijer (Marchal '97); and in still others the pupa is enclosed in a 

 delicate cocoon instead of in a puparium. 



The literature regarding this family is very extensive; hundreds 

 of articles have been written about those species that are of economic 

 importance, and very many papers have been published on the classi- 

 fication of these insects; A monograph of the species of the world was 

 published by Kieffer in 1813 and a review of the American species is 

 being published by Dr. Felt in his annual reports as State Ento- 

 mologist of New York. See also Felt (' 1 8) for descriptions and figures 

 of the galls produced by members of this family. 



The family Cecidomyiidce is separated into three subfamilies, 

 which can be separated by the following table : 



A. Ocelli present ; vein A^T, preserved either simple or forked, p. 8 16 . Lestremiin^ 

 AA. Ocelli wanting; vein M wanting or represented merely by a fold. 



B. Antennae without either circumfili or horseshoelike appendages; the first 

 segment of the tarsi usually longer than the second p. 8i6.Heteropezin^ 



