THE SUDDEN DISAPPEARANCE. 249 



By virtue of their naturally secretive habits, and of their 

 protective coloring, the worms in their earlier stages easily 

 escape the eyes of man ; but when the bulk of them have 

 passed through the last moult, or in other words are nearly 

 full-grown, and have stripped the fields in which they were 

 born, they are obliged to migrate in bodies to new pastures. 

 Thus assembled and exposed, they pass through grass and 

 grain fields, devouring as they go ; for they are now exceed- 

 ingly voracious, and, like most lepido^^terous larvae, consume 

 more during the last few days of worm-life than during all 

 the rest of their existence. The farmer who is unacquainted 

 with these facts naturally wonders at this sudden appear- 

 ance ; and shortly afterwards, when they enter the earth, or 

 otherwise conceal themselves to transform, he is again puz- 

 zled at their sudden disappearance. When the worms are 

 thus exposed in numbers, the many natural enemies of the 

 species work far more effectively than when they have to seek 

 individuals hidden here and there in the rank grass : hence 

 the partial annihilation of that species that follows the 

 advent of such large numbers. Moreover, while a certain 

 amount of moisture is most congenial to them, excessive rains 

 and floods, such as are likely to occur after very dry years, 

 must inevitably tend to their destruction, floating many away 

 into rivers, and causing others to rot on and in the ground. 

 Man, too, in his warfare with them on such occasions, de- 

 stroys great quantities. Finally, it is only the vast armies on 

 our cultivated lands that disappear so suddenly: numbers 

 yet remain unobserved in unfrequented and uncultivated 

 meadows and prairies. 



Whether the species produces one or more broods annually 

 had long been a disputed question. All the facts indicate, 

 that, over the larger part of the country in which it proves 

 injurious, there is but one brood annually ; but I have proved, 

 that, like so many other species that are single-brooded 

 farther north, it is double-brooded in latitude thirty-eight 

 degrees, having succeeded in rearing one generation from the 

 other. The second brood of worms gave me the moths early 

 in August ; and there is good evidence, that, exceptionally, a 

 third brood may be produced the same year. Indeed, by dili- 

 gent search out of doors, I have found larvae of all sizes dur- 

 ing the month of August, and a few full-grown individuals 



32 



