149 



of the Rocky Mountains, in Utah, Idaho, and their vicinity, migrating 

 when abundant into adjacent cultivated regions, which it desolates as it 

 goes. It has also appeared in Washington, Oregon, and Wyoming, but 

 never, as yet, on the eastern slope of the Rockies. 



These insects are rather long-legged, of a dull gray-brown color, the 

 upper surface of the thorax leathery, projecting backward, with a rounded 

 margin. In their migrations they press forward regardless of irrigation 

 ditches or other passable obstacles, and only a large stream can cause 

 them to change their direction. Their migrating armies are often very 

 large, ten to twenty miles long and one to three miles wide. The eggs 

 are laid in hard ground — probably about fifteen to eighteen in each lot — 

 in an elongate cavity made by means of the ovipositor. Egg-laying 

 begins in July and continues into September, individuals ovipositing at 

 intervals of several days. Migrations usually begin in July. Since the 

 country they invade is not their natural home they disappear after a 

 time, and nothing more is seen of them until the next migration. 



They can be herded like a drove of sheep and driven out of fields, 

 especially when young, but this must be done repeatedly. Being wing- 

 less and poor "high jumpers" they are easily stopped by low barriers. 

 A six-inch board with an overhanging strip of tin to prevent their 

 climbing over will completely check them, and the accumulating masses 

 may be crushed by a heavy drag drawn in front of the barrier. 



THE SOD WEB-WORMS. 



Various Species of Crambus, 

 Descriptive Distinctions. 



The accumulation, from time to time, of a considerable collection of 

 sod web-worms representing various localities, has given me a favorable 

 opportunity to distinguish species and to connect them, by breeding, 

 with the adult Crambus. The results of a study of this material, under- 

 taken at my request by my assistant, Mr. C. A. Hart, are presented here 

 for the information of entomologists. 



Dr. Felt has described* and illustrated the eggs of a large number of 

 New York species of Crambus, and also the young larvae which hatched 

 from them. Unfortunately these all died before reaching maturity. 

 Similar experiments begun at this office ended in the same way; and 

 even in our attempts to rear maturing larvae to the adult, the proportion 

 failing to complete their transformations was unusually large. In his 

 monograph of the North American species of the family,! Fernald has 

 included all published descriptions of their immature stages, among 

 them, those of Felt. As is usually the case, however, these independently 



*"0n Certain Grass-eating Insects." Bull. 64 (1894), Cornell Univ. Agr. Exper. Station. 

 t"The Crambidse of North America." Mass. Agr. ColL, 1896. 



