The Army-worm. 255 



these little parasitic flies, ever succeed in reaching the pupa stage; 

 usually the maggots of the parasites get full grown and leave the 

 caterpillar's body about the time it is also full-grown. The mag- 

 gots burrow into the ground beneath their host's bod)^ and in a 

 few days undergo their transformations to the adult fly. 



The deadly work of these tachina flies, of course, does not cul- 

 minate until the worms have done about all of their damage, but 

 the further development of the insect is stopped and thus the 

 danger of another brood of army- worms is averted. New York 

 farmers were greatly indebted to these little tachina flies last year, 

 or so effectively did they work on the July brood of worms that 

 we believe the comparative insignificance in the numbers of the 

 September brood was largely due to the efforts of the little flies 

 in July. In other words, had it not been for the work of these 

 flies in July, we believe many New York farmers would have suf- 

 fered from similar armies of the caterpillars in September. 



The question has been asked : What do these tachina flies 

 feed upon when the crop of army-worms is comparatively insig- 

 nificant ? The yellow-tailed tachina fly seems to have been bred 

 only from the army- worm, but the red-tailed species is known to 

 work upon at least thirteen other kinds of caterpillars.* Doubt- 

 less the former species also has other hosts, and thus when there 

 is a shortage in the army-worm crop, these tachina flies have 

 other choice delicacies in the worm line that may be substituted 

 in their menu. 



There are several species of minute four-winged flies which are 

 also parasitic upon the army-worm. The flies ' ' sting ' ' their eggs 

 through the caterpillar's skin, and the grubs that hatch live 

 within the body of their host ; when they issue, they spin small, 

 oval, white, silken cocoons attached by loose silk to some neigh- 

 boring object. As many as ninety-six of the grubs may find 



* Dr. L. O. Howard writes that this tachina fly has the following hosts : 

 Deilephila lineata Fabr. ; Protoparce Carolina L,inn. ; Phi/ampelus pandorus 

 Hueb. ; Alypia 8-maciilata Hueb. ; Attacus proinethea Drury. ; Attacus 

 cecropia Linn. ; Orgyia leiicostigina S. and A. ; Datatia ministra Drury. ; 

 Adoneta spivuloides H. S. ; Pcridroma saucia Hueb. ; Fcltia herilis Grote ; 

 Leucania tmipicnda Haw.; Laphygvia fnigiperda S. and A.; Hemaris dif- 

 finis Boisd. 



