284 REPORT UNITED STATES ENTOMOLOGICAL COMMISSION. 



cheeks are mottled with rust-brown and edged behind with yellow ; the head beneath 

 and palpi, except a black rim around tips, are pale yellowish. The other colors are 

 much as in the mature insects. With each succeeding stage the broad and pale streaks 

 of prothorax intensify, and as soon as the hind wing-pads are turned up over the front 

 pair, viz, in the fourth stage, the pale spot at the base, which becomes so conspicuous 

 in the pupa, is visible. The black face after the first molt is quite characteristic, and 

 often endures to the pupa state. (See PI. I.) 



Atlanis. — Aside from its smaller size, throughout its growth, this species may be dis- 

 tinguished as follows : In the first stage it is more uniformly and distinctly dotted 

 with black, the legs being strongly dotted and banded, and the hind thighs being 

 darker and showing much more distinctly the pale transverse streaks. In the second 

 stage, the color is more livid or rosy, with a more strongly contrasting yellow venter. 

 In the subsequent stages, these colorational differences still prevail, and the face is not 

 black as in sjjre^Ms; the pale spot on the hind wing-pads is less conspicuous in the 

 fourth stage, and the pupa is distinguished not only by its smaller size and different 

 color, but by the narrower, more obsolete black marks of the prothorax and by the 

 wing-pads being considerably shorter and smaller, the hind pair livid, with only rarely 

 a touch of black at base, and with the pale spot subobsojete. The pale streaks on the 

 outside of the hind thighs are always conspicuous. It jTresents, in fact, a marked con- 

 trast to the pupa of spretus. Atlanis invariably has a pale face — yellow or greenish, 

 speckled with gray-brown ; and, just as invariably, the outside of the hind thighs more 

 mottled with pale oblique streaks through the black. (See PI. III.) 



Femur-rubrum. — In size, intermediate between the otber two, this species is never- 

 theless easily distinguished from either. In the first stage, the spots of body and 

 bands of legs are subobsolete, and the hind thighs have no transverse streaks. In the 

 subsequent stages, it is distinguished by the generally paler and greener hue ; by the 

 black being more solid and intense and contrasting more with the pale colors ; by the 

 wing pads having no pale spot (or very rarely a faint indication of it), and by the 

 outer black mark on hind thighs showing no pale streaks. The face is pale through- 

 out and less speckled than in atlanis, and the upper white mark running from the side 

 of the prothorax is more conspicuous on the head behind the eyes than in the other 

 species. (See PL II.) 



CHAPTEE XI. 



INVEETEBRATE ENEMIES. 



THEIR VALUE. 



The good offices of the larger vertebrate animals, in assisting man to 

 overcome the devastations of the Eocky Mountain locust, will be set 

 forth in the succeeding chapter. Under the present head we shall con- 

 fine our attention to those smaller animals, belonging principally to its 

 own Class, which, though often invisible or scarcely perceptible, yet carry 

 on their good work most effectually. It is a law in nature that every 

 animal necessarily meets with checks of one kind or another to its undue 

 multiplication. Even the slowest-breeding species would soon overrun 

 all habitable parts of the globe to the exclupiou of others, were the coun- 

 teracting influences — the struggle between species for supremacy — that 

 keep it within bounds, by any possible means removed ; while the more 

 prolific species would do so in an almost incredibly short space of time. 

 Most plant-feeding insects are so prolific that, unchecked, they would 

 very soon annihilate the particular plants upon which they feed, and we 

 find them beset with many checks, not the least important of which are 

 their insect parasites and devourers. Let the plant-feeder once become 

 unduly multiplied, and these, its natural enemies, invariably multiply in 

 increasing proportion, until, in their turn, they get the upper hand, and 



