848 



AN INTRODUCTION TO ENTOMOLOGY 



The larvae of the different species differ greatly in habits, some 

 feed on decaying vegetable matter, dead insects, snails, etc. ; someara 

 common in mushrooms, and are sometimes a pest in mushroom cel- 

 lars; some are internal parasites of other insects, as bees, wasps, ants, 

 saw-flies, etc. ; several species are known to live in the nests of ants. 

 some as parasites and others as commensals. One of these Metopina 



^2±i_Rj + S 



Fig. 1099. — Wing of Phora. 



pachycondyle lives curled about the neck of its host ant-larva, par- 

 taking of the food given the latter by the attendant worker ants; 

 and one has been bred from an egg-sac of a spider. 



A monograph of the North American species of this family was 

 published by Brues ('03) and one by Malloch ('13). About 150 

 species have been described from this region. 



The Phoridae are classed among the Brachycera by some writers 

 and among the Cyclorrhapha by others. Morris ('22) states that 

 when the adult fly of a species studied by him, Hypocera incrassdta, 

 emerges from the puparium a circular cap, consisting of the skin of 

 the cephalic region and thoracic segments of the larva, is split off by 

 means of a fissure passing round the body between the third thoracic 

 and first abdominal segments. This confirms the opinion that this 

 family should be placed in the Cyclorrhapha. 



Family PLATYPEZID.E 



The Flat-footed Flies 



These flies resemble the house-fly somewhat in appearance but 

 are very much smaller. They hover in the air in shady places and 

 alight frequently on the leaves of low plants, where they run about 

 in circles with great rapidity. 



The head is hemispherical or spherical, and as broad as or broader 

 than the thorax. The antennas are three-jointed with a termiral 

 arista. The legs are short and stout, and the tarsi of the hinder pair 

 are often very broad and flat (Fig. iioo); but they vary greatly in 

 form in different genera. The wings are rather large, and when at 



