CircuLar No, 138. Issued April 22, 1911. 
United States Department of Agriculture, 
BUREAU OF ENTOMOLOGY. 
L. O, HOWARD, Entomologist and Chief of Bureau. 
THE ALFALFA CATERPILLAR. 
(Hurymus curytheme Boisd.) 
By V. L. WILDERMUTH, Agent and Expert. 
INTRODUCTION. 
The insect under consideration in this circular is the caterpillar 
(fig. 1) of one of our most beautiful and common butterflies (figs. 2, 
3) belonging to the group known as “the yellows,” and is closely re- 
lated to the well-known cabbage butterfly. The name “ yellows” at 
once gives one an idea of the 
appearance of the adult, but 
this may be misleading, as the 
species is polymorphic, the 
coloration Varying from a Frio, 1.—The alfalfa caterpillar (Eurymus eury- 
bright vellow (very fre- theme) : Larya or caterpillar stage. About 
P twice natural size. (Original.) 
quently noticed), through an 
orange-sulphur (the most commonly noticed), to a pale white (the 
least often noticed). 
For some years past the green caterpillars of this butterfly have 
been reported from various localities in the southwestern United 
States as feeding on, and in some cases doing a large amount of 
damage to growing alfalfa (J/edicago sativa). It should be men- 
tioned here that it is the caterpillar or worm stage of this species that 
does the damage, and not the adult butterfly. The latter feeds on 
the nectar of the bloom and in no way injures the plant. In fact, the 
writer has noticed these butterflies to all appearances springing the 
pollen triggers on the alfalfa blossoms while feeding, thus, should 
his observations prove correct, benefiting the plant for seed produc- 
tion. In the year 1906 a correspondent of the Department of Agri- 
“Though the author is quite confident of the accuracy of his observations, it 
is a case where misconception is exceedingly liable to occur; if correct, however, 
the fact is entirely new. See Dr. I. Urban, Verhandlung des Botanischen 
Vereins der Proving Brandenberg, 1872, p. 13; Herman Muller, The Tertiliza- 
tion of Flowers, par. 93 and 94, 1878: C. V. Piper, Report of American Breeders’ 
Association, 1909, Report of Committee on Breeding Forage Crops—I. M. 
WEBSTER. 
(Cir. 133] 1 
