418 



NORTH AMERICAN DIPTERA 



of them are attracted to light. "Honey dew" is very attractive to many 

 of the species. The adults are frequently very busy creatures and many 

 females seem to fly incessantly in search of a suitable host for their off- 

 spring. 



It is extremely unfortunate that this important family is in such 

 a hopeless state taxonomically. The forms I include were at one time 

 placed in two distinct families, the Tachinidee and Dexiida, and some 

 authors have recognized a number of families for the group. The Dexiids 

 were separated because of the plumose or haired arista but the charac- 

 ter is not of value. During my studies of this family I have searched in 

 vain for reliable characters by which to differentiate groups. Many 

 characters are good up to a certain point but beyond that they cease to 

 be of real value. In many genera the propleura is haired but in some 

 this character is not reliable. The same is true in regard to the hairiness 

 of the lower squamal lobe, a character occurring in but a few genera in 

 the world. The chgetotaxy is variable and there is every gradation be- 

 tween extremes. 



Complex antennae found in Tachinidse. 



The question of generic limits in this family is a most perplexing 

 one. No two people have the same conception of, generic limits and it 

 will be found that I disagree in many respects with Townsend, Ville- 

 neuve, Aldrich and others, although agreeing rather well with Dr. 

 Aldrich. I have been unable to correlate all of Townsend "s genera with 

 my conception of genera but I have indicated, in the index, a great many 

 which I think should be placed in the synonymy. It might be, of course, 

 that I have gone too far in reducing the number of described genera 

 and that some of those relegated to the synonymy should be recognized 

 as distinct. I feel, however, that the number of genera recognized is 

 still too large and that we may safely reduce it to the benefit of the 

 taxonomy of the family. It is true that in the present work I have 

 added a number of new names and my excuse for doing so is to be 

 found in the fact that I am unable to place the species in any described 



