106 REPORT 4, UNITED STATES ENTOMOLOGHCAL COMMISSION. 



site. This last, as soou 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 

 changes to a bright bluish-green. The growth ofthelarvais 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 this time showed no signs of being af- 

 fected, except by its sickly yellowish color and 

 by its very slow growth, collapses and dies as ^ ^^^- 34. -Larval skin of Aietia 



'^ i; C5 7 X fastenf'd to a leaf by Euplectrus 



soon as a single one of the parasitic larvae cocoons. (Original.) 

 withdraws, and the same fate overtakes those Euplectrus larvse which 

 are at the time less advanced in their development or immature. If one 

 of the parasitic larvse be removed by hand, both the victimized worm 

 and the remaining parasites quickly dry up. The parasitic larvse 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 i)reparing 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 emx^ty skin, to the leaf. As the Euplectrus latvae 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 

 tlie Euplectrus larvae consists of an irregular m^esh 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. 31.) Protected by the caterpillar 

 skin as by a roof, the Euplectrus larva changes to a pupa, the color of 

 w^hich 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 {ElacMstus euplectri)^^'^ and its x^upa is 

 sometimes destroyed by another enemy, ijrobably some Carabid beetle. 

 It is very common in the vicinity of Selma, and in October, 1880, in 

 company with the Apanteles aletkc, it caused the almost complete de- 



