188 EEPORT OF THE COMMISSIONEE OF AGRICULTURE. 



The liabits of the -worms are somewliat like tliose of their relatives, 

 the cut-worms, in that thej' feed chiefly at night. During the heat of 

 the day they hide under sticks, stones, or other rubbish, though, when 

 occurring in great numbers, they often eat during the entire day or dis- 

 appear only for a few hours. When migrating from an eaten field to a 

 new one they have the habit of going together and nearly always in the 

 same direction, which has given them their popular name of " army- 

 worm." Their food plants are naturally the grasses and grains. Dur- 

 ing the present i^eason they have usually appeared first in fields of 

 wheat, occasionally in timothy and blue grass, seldom in any other cul- 

 tivated crop. When on the march they attack i)referably the cereals, 

 timothy, blue grass, and corn. Many other plants are eaten to a small 

 extent. Shortly after the last moult the worm burrows just beneath 

 the surface of the ground, and transforms to a pupa in the cell thus 

 formed. 



The pupa is dark brown in color and is from 18 to 20™™ (three-quarters 

 of an inch) in length. Its shape is shown in PI. I, fig. 1. 



The numher of generations in a season varies greatly with the climate. 

 It has always been supposed that there is but one in the Northern 

 States, but there will probably be two on Long Island this year, as moths 

 are now (June 21, 1880) emerging from pupae collected there a few days 

 ago. Professors Thomas and French state that there are normally two 

 broods in IsTorthern Illinois, and probably three in the more southern 

 portions of that State. Professor Eiley has demonstrated two broods 

 normally and three broods exceptionally in the latitude of Saint Louis. 

 Farther south, during winters of unusual mildness, a succession of 

 broods is kept up through the entire year. During the present winter 

 (1879-'80) we have received full-grown worms with accounts of damage 

 to winter grain in the months of December, January, and February 

 from localities as far north as Union County, South Carolina, and Marion 

 County, Tennessee. Ordinarily, however, in these States, and always 

 farther north, the insect lies dormant through the winter months. 



Concerning the hihernation of the army worm writers have long differed. 

 We can now safely state that it hibernates both in the moth and chrys- 

 alis states, the former being more common in the southern part of the 

 country and the latter in the northern regions.* There is also a possi- 



* Since tlie days of Walsh, no one has strongly upheld the probability of an exten- 

 sive hibernation of the eggs. We may briefly state the arguments which have been 

 advanced in favor of hibernation in each stage as follows: 



Egg hihernation. — In fields which have been burned over in fall or winter the worm 

 does not appear the following year. (Many cases cited by Walsh and Riley.) Walshi 

 (Prairie Farmer, 1861) states an instance where one-half of an infested field was burnedl 

 over and the other half not. The succeeding year the burned half was free from worms 

 and the other was infested. Against this argument Thomas (/6irf.) urges that the 

 moths appear in early spring and oviposit on old grass stubs before the young grass 

 has grown ; naturally, therefore, where the old grass has been destroyed they will 

 not lay their eggs. Riley cites the Wisconsin fires of 1871, which occurred in Oc- 

 tober, not\A'ithstandiug which the worms were very abundant the succeeding year in 

 the same localities. 



Larval Mbernation. — All European species of Leucariia, so far as known, hibernate as 

 larvae. Many allied cut-worms hibernate in this state. Against such hibernation 

 Riley urges that, instead of wet springs being favorable to increase (as has been sup- 

 posed to be the case), were there an extensive larval hibernation such weather would 

 be the most unfavorable, as the overflowing of swamp land would drown them. 



Pupal hihernation. — Moths are found in early spring in such fresh condition, with 

 wings so soft that they have evidently just emerged from their pupal cases. Mr. Meske, 

 of Albany, N. Y., once found a chrysalis in May, from which a true army-worm moth 

 issued, the date being so early as to xjrecludethe possibility of a brood having already 

 been generated. Professor Riley urges the instance of the Wisconsin fires in favor of 

 this method of hibernation. Many allied Noctuids are known to hibernate in this form. 



