2 BULLETIN 124, U. S. DEPARTMENT OF AGRICULTURE. 
the Southwest, placing on this species the blame for injury to alfalfa, 
were doubted. In the spring of that year, however, the writer was 
detailed to investigate these reports in the Imperial Valley and 
discover whether the butterflies bore any relation to the destruction 
of alfalfa by a " green worm." His observations showed that the 
accusations were well founded, for in July, 1910, the butterflies were 
seen to lay the eggs that hatched into the green larvse which ate up 
the alfalfa crop, causing a loss of thousands of dollars. 
At the end of the first year's investigation, experiments and ob- 
servations had been completed which were thought to be of immediate 
benefit to the ranchers in controlling the pest, and a preliminary 
report was made and published as Circular 133 of the Bureau of 
Entomology. During the three years subsequent to this preliminary 
Fig. 2. — The alfalfa caterpillar : Full-grown larva. Enlarged about three diameters. 
(Original.) ___ 
investigation the writer and others have made a more exhaustive 
study of the species, its habits, and natural or artificial methods of 
control, and the object of this bulletin is to record these observations 
as they' have been interpreted. 
GENERAL DISTRIBUTION. 
According to Scudder 1 this insect is well distributed over the 
United States, but is found in its greatest numbers in the Mississippi 
Valley (see map, fig. 3) and to the westward. In only a few cases 
does it appear east of the Allegheny Mountains, but its range ex- 
tends northward into Canada, even as far as Hudson Bay. In 1911 
Mr. R. A. Vickery made observations on the species at Brownsville, 
Tex., thereby considerably extending the southern range from that 
included in Scudder's map. In past years the species has been espe- 
cially abundant throughout the alfalfa -growing sections where irri- 
gation is extensively developed. 
1 Scudder, S. H. The Butterflies of the Eastern United States and Canada, v. 2, Cam- 
bridge, 1889, pp. 1131-1132. 
