REPORT OF THE ENTOMOLOGIST. 189 



bility that the full-growu worms hibernate more or less frequently. In 

 either case, as soon as the weather becomes warm in spring the moths 

 emerge either from their pupal cases or their hibernating quarters, and 

 lay their eggs as before described. The duration of the egg state is 

 from eight to ten days. We found the newly hatched larvae in Wash- 

 ington on the 13th of May, 1879. 



The natural habitat of the army worm was stated by Dr. Fitch to be 

 " in the wild grass of wet spots, in swamps and on the border of marshes," 

 and in this statement he has been followed by nearly all succeeding 

 writers. The question then naturally arises. What is the cause of these 

 sudden and extensive periodical visitations to cultivated crops ? Dr. 

 Fitch observed that the year 1861 was very wet, while that of 1860 had 

 been extremely dry. On examining the records he found that in pre- 

 vious worm years the season in which the worms appeared was wet, 

 while the preceding year was dry. He therefore proposed the theory 

 that in a dry season this insect, having an unlimited extent of feeding 

 range, becomes greatly multiplied, " and when it is thus multiplied, a wet 

 season and overflowed swamps drive it out from its lurking place, in 

 flocks, alighting here and there over the country. But on being thus 

 rusticated, it finds our arable lauds too dry for it, and immediately on 

 maturiug and getting its wings again it flies back to the swamps, whereby 

 it happens that we see no more of it." Professor Eiley adopted this 

 theory, and showed that the conditions in 1869 and 1875 (two marked 

 army worm years) coincided with those mentioned by Fitch. 



HOW TO DESTROY THE PEST. 



Remedies. — If the theory just quoted be. true, the best means of pre- 

 venting the occurrence of this pest in cultivated fields will be to keep 

 watch of any extensive tracts of low land which may be in the neigh- 

 borhood, and if army worms are discovered destroy them either by 

 burning over the laud, if possible, or by poisoning with arsenic, Paris 

 green, or London puiple, or by any other means of which the local con- 

 ditions will admit. In fact it would be well to burn over all the low land 

 in the vicinity each winter, thus destroying the hibernating insects. 



I do not feel implicit confidence, however, in the above theory, as I 

 have observed the army worms feeding in small numbers in meadows 

 on high lands, when their presence there could not be explained by the 

 reasons given. Moreover, from what data I have been able to obtain 

 while preparing this article, it appears that the present season has not 

 been a wet one in those localities in which the army worm has appeared, 

 thus failing to confirm the theory. It is worthy of note, however, that 

 in most instances the localities infested by the worm this year are in the 

 vicinity of extensive tracts of low lands. I am carefully collecting evi- 

 dence on these points and wUl publish the results as soon as practicable. 



In case the worms do appear in cultivated lands the best plan of ac- 

 tion to follow is to prevent the spreading of the insect. This may be 

 done by destroying tliem or by confining them to the fields in which they 

 appear. The best methods of destroying them are by crushing with 

 rollers or by poisoning with arsenic, Paris green, or London puri)le. Either 

 of these substances can be apijlied rapidly by mixing with -water and 



Hibernation as molhs. — Of this there can be no doubt. Specimens have been received 

 at this department from Texas, Alabama, and Georgia all through the ■winter. " Some 

 specimens captured in the spring in Southern Illinois have a battered and weather- 

 worn appearance." (French.) Mr. Strecker has found the moth hibernating in Feb- 

 iruary at Reading, Pa., and l.Ir. Mann has also found it at Cambridge, Mass. 



