DIPTERA 



837 



Family ACROCERID^'' 



The Small-headed Flies 



These flies are easily recognized by the unusually small head, the 

 ^arge humpbacked thorax, the inflated abdomen, and the very large 

 alulets (Fig. 1078). The body is devoid of bristles 

 and the empodia are pulvilliform. 



The head is composed almost entirely of eyes, 

 and in some genera is minute. The eyes are contig- 

 uous in both sexes or nearly so. The antennae are 

 three-jointed, and are furnished with a style or an 

 arista in some genera, in others not. Sometimes the 

 antennse are apparently two-jointed, the first seg- 

 ment being sunken in the head. The venation of 

 the wings varies greatly in the different genera. The accompanying 

 figure (Fig. 1079) represents a single genus rather than the family. 



The flies are generally slow and feeble in their movements. In 

 some species that feed upon flowers the proboscis is very long, some- 



Fig. 1078.— 

 Pterodontia 

 misella. 



Fig. 1079. — Wing of Eulonchus. 



times exceeding the body in length. Other species take no nourish- 

 ment in the adult state, and have no proboscis. 



The larvag of only a few members of this family have been ob- 

 served; these are parasitic in the egg-sacs or in the bodies of spiders. 

 The life-history of an American species, Pterodontia flavipes has been 

 described by King ('16). The females of this species deposit their 

 eggs on the bark of trees ; they produce a large number of eggs ; in one 

 of the cases observed these numbered 3,977. This production of many 

 eggs is doubtless an adaptation made necessary by the fact that many 

 of the young larvae will fail to find spiders to attack and will conse- 

 quently perish. A larva that succeeds in finding a spider bores into 

 its body and there lives till fully grown ; it leaves the body of its host 

 to transform. 



''This is the family Cyrtidae of some authors ; but Acroceridae is the older name. 



