The Bulletin. 37 



adult moth state, the moths laying eggs in early spring in grassy places, 

 each female moth being capable of laying several hundred eggs. The 

 worms which hatch from these feed on grasses, and when the supply is 

 exhausted may march in an ''army" into corn or other grain. They feed 

 eagerly, groAv rapidly, and finally enter the earth to change to the pupa 

 stage, from which adult moths emerge in two weeks, and these, after 

 mating, lay eggs for another brood. 



When searching for new food they often move in a solid army con- 

 taining countless thousands of individual worms, and devour all suit- 

 able food as they go. The records that we have for this State indicate 

 that they have destroyed corn, grasses, and timothy; but wheat, oats, 

 millet, etc., are also relished. Their preference seems to be for the grass- 

 like plants; but in absence of these, they may be induced by hunger to 

 take others. 



Natural Enemies. — Fortunately, this Army- worm seems especially 

 susceptible to subjection by its natural enemies, among which the most 

 important seems to be a parasitic fly ( Winthemia Jk-pustulata, Fab. Or- 

 der Diptera). This fly is somewhat larger than a house-fly and more 

 bristly. It lays its eggs on the skin of the Army-worm and the fly- 

 maggots hatching from these eggs eat into the body of the worm, usually 

 causing its death before it can reach the adult moth stage to perpetuate 

 another brood. 



Mr, Z. P. Metcalf, at that time assistant in this office, made observa- 

 tions on the activity and efficiency of these parasites during the Army- 

 worm outbreak at Durham in August, 1908. Out of 491 worms which 

 Mr. Metcalf brought back and confined in cages, 442 were infested with 

 eggs of this parasite, leaving 49 without parasites, — yet 61 of the worms 

 developed to the pupa, but only 7 yielded adult moths. In a few cases 

 he found that where only a single egg had been fastened to the worm, 

 that it was able to complete its changes and emerge as an adult moth. 

 But the fact of only 7 moths developing from 491 worms indicates that 

 over 98 per cent of the worms died before reaching maturity, w^hile from 

 these same 491 worms he reared 556 adults of the fly-parasite. His data 

 showed that while many of the parasites also died before they matured, 

 that the rate of mortality with the Army-worm was over 98 per cent, 

 while for the parasite it was 73 per cent. This difference would un- 

 doubtedly be much greater could the rate have been calculated from egg 

 to adult in both cases; but this was impossible. But these results show 

 that the tendency would be for the flies to rapidly overtake the worms 

 in number, and subdue them; and this, no doubt, in large measure ex- 

 plains why the Army-worm is not more often destructive, and why it is 

 that usually only one destructive brood shows up in a locality in any 

 one season. 



