DIPTERA OF MINNESOTA. 



157 



fruit and shade trees, vegetables, grain, etc. The female lays her 

 eggs upon the caterpillar, and the young maggot, upon hatching, 

 bores its way into the tissues of its host, where it lives until full 

 grown. A caterpillar so attacked, and very many are thus afifect- 

 ed, is sure to die. The white eggs of these useful flies can frequent- 

 ly be, seen upon caterpillars, looking much like the representation 

 in Fig. 150, which shows on the right two caterpillars upon which eggs 

 have been laid. This is a common species, and has been bred from 

 at least fourteen difl:'erent host species, among them the common 

 large Cecropia moth. This species also occurs in Europe. There 

 is no question but that this family, from its parasitic habits and 

 abundance, is practically first in importance among insects which 

 ai? indirectly beneficial to man. While they frequently waste their 

 eggs by depositing them in undesirable places, they compensate us 

 by choosing a great variety of victims from among injurious insects, 

 a single species of Tachina fly having been known to parasitize in- 

 sects of two or three difl^'erent orders. It must be confessed, how- 



Fig. 151. Side view of fly shown in l"ig. 150. Original. 



ever, that under certain conditions some of the members of this 

 family injure us by attacking insects which are useful. Ugimyia 

 sericariace, for example, in Japan attacks the silk worm. It is believed 

 that this cunning fly lays its eggs on the mulberry leaves which are 

 eaten by the silk worm. As many as five of the maggots of this fly 

 may be found in one worm, of which rarely more than one is said 

 to reach maturity. 



These flies, which are so generally useful in this state, are gen- 

 erally grayish or black, or gray and black. The largest one in our 

 collection is nearly or quite an inch long. This species, Echinomyia 



