106 REPORT 4, UNITED STATES ENTOMOLOGICAL COMMISSION. 
site. This last, as soon as it has freed its head from the egg-shell, 
pierces the skin of its victim and thereafter remains stationary with its 
head buried. As soon as it has fairly begun to feed the white color 
chau ges to a bright bluish-green. The growth of the larva is very rapid, but 
seems to vary according to the season, averaging three days in August 
and four days in September. When full-grown, the larvae crowd each 
other, and if there are five or more of them on a caterpillar they form a 
semi-globular lump of very striking appearance. (Fig. 33.) Usually their 
growth is uniform, and retardation in develop- 
ment of individuals in the group results in 
death. When full-grown they turn yellowish- 
white and relax their hold. The worm, which 
up to tiiis time showed no signs of being af- 
fected, except by its sickly yellowish color and 
by its very slow growth, collapses and dies as * FlG - 34.-Larvai skin of Aietia 
J ^ o 7 -f fastened to a leaf by Euplectius 
soon as a single one of the parasitic larvae cocoons. (Original.) 
withdraws, and the same fate overtakes those Euplectrus larvae which 
are at the time less advanced in their development or immature. If one 
of the parasitic larvae be removed by hand, both the victimized worm 
and the remaining parasites quickly dry up. The parasitic larvae always 
remain stationary on the worm which the parent fly has chosen as its 
victim, and they never even move from the spot where the egg has been 
laid until they are full-grown. Every attempt made to transplant a 
parasite from one worm to another invariably resulted in the death of 
the parasite. 
In preparing for pupation, the larvae manage, by a peculiar elonga- 
tion and sudden contraction of their abdominal joints, to work from 
the back of the worm to the ventral or attached side, where they spin 
fine, silken threads which more fully secure the worm, which is now 
a mere empty skin, to the leaf. As the Euplectrus larvae take their 
places side by side, the caterpillar skin is fastened its whole length to 
the leaf, if there are five or more of the parasites ; but if there are fewer, 
only one portion of the skin, usually the anterior end, is fastened, the 
remaining portion either hanging down or breaking off. This web of 
the Euplectrus larvae consists of an irregular mesh of yellowish-white 
silk, recalling some kinds of mold, and is spun to secure the caterpillar 
skin to the leaf, in addition to a few other threads to prevent the pupa 
from being moved from its place. (Fig. 34.) Protected by the caterpillar 
skin as by a roof, the Euplectrus larva changes to a pupa, the color of 
which is dark honey-yellow, with the head and abdomen very soon be- 
coming pitchy black. The duration of the pupa state varies from three 
to eight days. The Euplectrus is subject to the attacks of a secon- 
dary parasite of its own family (Elachistw eupkctri)* 1 and its pupa is 
sometimes destroyed by another enemy, probably some Carabid beetle. 
It is very common in the vicinity of Selma, and in October, 1880, in 
company with the Apanteles aletice, it caused the almost complete de- 
