ITS NATURAL ELEMENTS. 251 



cording to latitude and the character of the seasons, there is 

 nothing to preclude its hibernating in any one of the four 

 states of its existence ; that, in the same latitude and under 

 the same conditions, it will even hibernate in different states ; 

 and that, finall}^, the great bulk of them hibernate in the 

 pupa and moth states, the proportion of the former increas- 

 ing northward. 



Of natural enemies the army-worm has no lack. Hogs, 

 chickens, turkeys, small birds of various species, toads, and 

 frogs, all feast upon it greedily whenever it appears in 

 considerable numbers. Various predaceous beetles likewise 

 gather around the travelling hordes, and prey savagely upon 

 them. Ten different species have been detected by myself 

 and others in this work. The worms have also an unusual 

 number of true parasites. They never travel from one field 

 to another unaccompanied by a number of tachinid flies, 

 which are often so numerous, that their buzzing is suggestive 

 of a swarm of bees. These are Exorista leucanice (Kirk) and 

 E. flavicanda (Riley). Seizing the first opportunity to attach 

 their eggs behind the heads of the army-worms, these flies 

 are as persistent in their work of destruction as the worms 

 are restless under attack. No worm carries these eggs into 

 the ground with it, but falls a victim to the maggots hatch- 

 ing therefrom, and which in a very short time become flies 

 like the parent. 



Often fully eighty per cent of the worms are parasitized 

 by these flies. 



The next most common parasite of the army-worm is Mi- 

 crogaster militaris (Walsh), — a little black, braconid fly, 

 with rufous legs. The larvae of this fly infest the worm in 

 great numbers, and so enfeeble it, that it cannot enter the 

 ground, but lingers, sluggish and paralyzed, on some grass or 

 grain stalk. Presently the little parasites all issue from its 

 body, and spin in concert a large amount of silk, in which 

 each individual forms a neat little egg-like cocoon. 3Ieso- 

 chorus vilreus (Walsh) is another braconid that attacks the 

 army-worm. It is but slightly larger than the preceding, and 

 may be distinguished from it by the more graceful forjn, and 

 by a translucent, yellowish-white spot in the middle of the 

 abdomen. Pezomachus minimus (Walsh) is a small, wingless 

 ichneumon, which, like the Microgaster^ spins cocoons in cot- 



