192 INSECTS AFFECTING VEGETATION 



as timothy and the small grains and cutting off the stems just below 

 the head. 



The adult insect is a pale or yellowish-brown moth, with a white 

 spot on the center of each fore-wing. Its minute white eggs are 

 usually laid in numbers from two to three to twenty in strings be- 

 neath the sheaths of grass stems, a strong effort evidently being made 

 by the female moth to conceal her litter. They are occasionally de- 

 posited also in other situations or beneath the leaf sheaths or loose 

 bark of other plants. The eggs hatch in from eight to ten days, and 

 the young caterpillars feed for a time in the fold of the leaf, but grow 

 rapidly and soon consume entire leaves. 



Under ordinary circumstances the larvse feed mainly at night, or 

 in damp, cloudy weather, remaining hidden during bright days, re- 

 sembling in this habit the closely allied cutworms. They reach full 

 growth in three or four weeks, attaining a length of 1^4 inches, bur- 

 row into the ground, and transform into brown chrysalides. In this 

 condition they remain in the summer an average of two weeks before 

 yielding the perfect moths. 



Several generations are produced each season; two or three in 

 the Northern States and four or five or perhaps six in the Southern 

 States. The army worm, as a rule, passes the winter in the half- 

 grown larval condition, occasionally in the South hibernating as a 

 moth, and perhaps rarely in the egg stage. 



This insect is present in grass land probably every year in 

 greater or less numbers, but on account of the habit of concealment 

 of the larva it is very rarely noted. It attracts attention and becomes 

 a matter of grave concern only when, as a result of a series of favor- 

 able years or exceptionally favorable local conditions, it suddenly de- 

 velops in enormous numbers and is forced by scarcity of food and 

 hunger to migrate in swarms from its breeding grounds, and travels 

 and feeds both during the day and night. 



The over-wintered larvse appearing suddenly in spring may oc- 

 casionally attract notice, but as a rule the notable and destructive 

 swarms are the progeny of the first, second, or third summer broods. 

 In general, it may be said that these \vorms are more apt to make 

 an injurious appearance in a rainy spring or early summer following 

 a season of comparative drought. 



As already noted, the fact that the army worm occurs at very- 

 irregular intervals usually widely separated, and as a rule without 

 warning renders it impracticable to get farmers to undertake pre- 

 ventive measures. In general, however, it is true that clean cultiva- 

 tion and the adoption of a regular system of rotation of crops in 

 which grass lands are alternated every few years with cultivated fields 

 will keep this insect in check and probably prevent an unusual mul- 

 tiplication of it. Bearing in mind also me fact that it breeds nor- 

 mally in rank grass and over-winters in such situations, it is of im- 

 portance to burn over such tracts early every winter, which will kill 

 many of the larvse and leave the others to be destroyed by exposure. 

 If these measures be practiced the army worm will probably never be 



