The Tachina Flies 



for example, seem to know by a touch of their antennae whether 

 or not an insect has already been stung by some other parasite and 

 they only in very rare instances insert an egg in the body of an 

 insect that already contains an egg or larva of another parasite. 

 Moreover, the ichneumon flies seem to grade the number of eggs 

 which they lay in a certain insect to the number of larvae which 

 can successfully grow within it. But the tachina fly will attach 

 to a caterpillar three or four times as many eggs as the number 

 of larvae the caterpillar can maintain. Thus many tachinid larvae 

 perish for want of food while some, which are barely able to exist, 

 produce flies which are dwarfed in size, so that some adult flies 

 are only one-third as large as others. 



As above stated, the group is a very large one and fortunately 

 it has been admirably monographed by Mr. D. W. Coquillett, 

 who has also brought together from the records of the U. S. 

 Department of Agriculture an interesting table of these flies in 

 relation to the insects upon which they have been parasitic. 



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