THE DIPTEROUS PARASITES OF ALETIA. 
109 
the lame of Phora, some the larva of this Cyrtoneura, while the largest portion con- 
tain only a badly smelling fluid. If further observations prove that this fly infests 
only such chrysalides and cannot be bred from the living Aletia larva, it cannot be 
considered a true parasite. — C. V. Rttqj. 
Tub Tachina Flies. — The other Dipterous Hies belong to the genus 
Tachina. The first of these was described by us in the Canadian En- 
tomologist, 1879 (Vol. XI, p. 1G2) as Tachina aletia:™ and is the most 
abundant Dipterous enemy of Aletia. It measures about one-third of 
an inch in length, and is more robust and sligjitly larger than the com- 
mon house-fly, from which, as well as from the Sarcophaga (which is 
less robust than the Tachina), it maybe distinguished by having the 
bristle of the antenna' smooth and not hairy. These Tachina llies are 
more completely parasitic- than the flesh-fly above mentioned, and their 
eggs are harder, more polished, and very firmly attached to the worm, 
usually just behind the head, where tin y cannot be molested. The 
larva- or maggots have the same habits and 
mode of transformation as those of Sarcophaga, 
and the accompanying figure (Fig. 38) of Ta- 
china fiavicauda Kilev, will serve to illustrate 
the llies. ( )ccasionally these maggots are not 
lull fed, and do not destroy the Aletia till 
after it has assumed the chrysalis state, but 
ordinarily they LS8U6 from the worm itself, 
which is frequently infested by more than 
tta. :;s.-v, iiow t;.ii. .i Taclitaa By. one. The species was reared from chrysalides 
sent by Mr. < 1 rote from Savannah and by others 
from various parts of the South, including the States of Alabama, Mis- 
sissippi, and Texas. 
Another species of Tachina has been described by Professor Comstock 
(Annual Report Of Commissioner of Agriculture, 1879, p.303) 36 as T.fra- 
tcrna, resembling T. aletia quite closciy. but found to differ upon careful 
examination. 
The number of worms killed by these Tachinid llies is very hard to es- 
timate. Their eggs are very common on the bucks of the cotton cater- 
pillars, especially towards the end of the season, occasionally as many 
as S or 10 eggs being found upon a single worm. Observers have esti- 
mated at different times the proportion of worms thus parasited, and it 
has occasionally reached as high as 40 per cent. ; but all who have ob- 
served these parasites at all have been struck by the fact, in the first 
place, that a very large number of the eggs are discarded with the cast- 
off skins at molting, and so the larva? which hatch die for want of sus- 
tenance, and, in the second place, that the Tachinid larvae destroy one 
another quite as readily as they feed upon the caterpillars. It is true 
that Mr. Trelease has recorded an instance in which a skin was shed 
without removing an egg, but this we must regard as exceptional. The 
