120 SECOND ANNUAL REPORT OP 



resemblances to one another, and in some cases it is not eas3' to sep- 

 arate them without knowing the larvae. Our Cottonwood species has 

 never been described. It bears a strong resemblance to several 

 European species, but as it would only weary the general reader to 

 give the details wherein it differs from those already described, which 

 closely resemble it, these details will be found to accompany the 

 scientific description below. 



This insect would undoubtedly become much more numerous 

 and troublesome, were it not for the fact that it is pursued by three 

 distinct parasites. Many of the worms when full grown will fasten 

 themselves firmly to a leaf in the curled position, and from the body 

 will issue from thirty to forty little maggots. These maggots are 

 each of them 0.17 inch long, of a dull green color, tapering each way, 

 with a dark dorsal mark, a lateral elevated ridge, and a row of shiny 

 elevated spots of the same color as the body between this ridge and 

 the back. Each one spins a mass of white silk around its body, and 

 creeps out of it and commences spinning afresh, until at last a large 

 aggregate amount of flossy silk is spun, into which the maggots work 

 back to transform, though some transform while lying on the surface. 

 These maggots eventually produce a little black Ichneumon-fly be- 

 longing to the genus Microgastcr.* Another and larger unde- 

 termed Ichneumon-fly belonging to the genus Ojihion, also attacks 

 this Cottonwood worm, and it is also occasionally infested with a 

 Tachina-\\y larva. 



These worms are most easily destroyed when young, for though 

 not strictly gregarious, they do not then scatter much from the 

 branch upon which they were born. 



Acronycta popcli, N. Sp. — Larva — Length 1.50. Color yellowish-green, covered with long soft, 

 bright yellow hairs which spring immediately from the body, part on the back, and curl round on 

 each side. On top of joints 4, 6, 7, 8 and 11, a long straight double tuft of black hairs, those on 7 

 and 8 the smallest. Head polished black with a few white bristles. Joint 1 with a black spot 

 above, divided longitudinally by a pale yellow line, giving it the appearance of a pair of triangles. 

 Joint 2 with two less distinct black spots. Thoracic legs black ; prolegs black with brownish ex- 

 tremities. Venter greenish-brown. Described from many specimens. When young of a much 

 lighter color, or almost white, with the black tufts short but more conspicuous, with a distinct 

 black dorsal line, two lateral purplish-brown bands, and with hairs white, sparse and straight. 



Individuals vary much : some have a black dorsal line, some have but three distinct black 

 tufts ; some have a Cth tuft of black hairs on joint '.), and others have a few black hairs on all but 

 the thoracic joints. Just before spinning up, many of the hairs are frequently lost, and the body 

 acquires a dull livid hue. 



Moth. — J, Front wings, white, finely powdered with dark atoms which give them a very pale 

 gray appearance ; marked with black spots as follows : a complete series of small spots on posterior 

 border extending on the fringes, one between each nerve; near the anal angle between nerves 1 and 

 2 a large and conspicuous spot bearing a partial resemblance to a Greek psi, placed sidevvise, and 

 from this spot a somewhat zigzag line running parallel with posterior border, but somewhat more 

 arcuated towards costa, least distinct between nerves 3 and 4, and forming a large distinct dart- 

 like spot between nerves 5 and 6 ; space between this line and posterior border, slightly darker 

 than the rest of the wing-surface on account of the dark atoms being more thickly sprinkled over 

 it ; four costal marks, one subobsolete in a transverse line with the reniform spot, one conspicuous 

 about the middle, and in a line with reniform spot and anal angle, one about the same size as the 

 last and looking like a blurred X about one-third the length of wing from base, and one subob- 



*MUroga$tcr acronycta of my MS. 



