THE 



DIPTEROUS PARASITES 



OF 



NORTH AMERICAN BUTTERFLIES. 



BY S. W. WILLISTON, NEAV HAVEN, CONN. 



But wlien he spitle the joyous Butterflie 

 In this laire plot dispacing to and fro, 

 Feareles of foes and hidden jeopardie. 

 Lord! how he gan for to Ijestirre him tho, 

 And to his wicked worlce each part applie ! 

 His heart did yearne against his hated foe, 

 And bowels so with ranlsling poyson swelde, 

 That scarce the sliin the strong cantagiou helde. 

 Spenskr.— Jlfiito^otmo*. 



Not many species of Diptera are known to be parasitic upon butterflies, 

 either in Europe or America, and they are all, with the exceptions noted 

 below, included in one f:\mily, the Tachinidac. In Europe, about fifteen 

 species have been bred and recognized, belonging to the genera Tachina, 

 Masicera, Exorista, and Phorocera. Others have been described by Rob- 

 ineau Desvoidy, but the diflficulty, if not impossibility, of recognizing this 

 author's species detracts almost wholly from tlie value of his observations. 

 Doubtless there are many more to be recognized in Europe, yet we can 

 hardly expect as large a number as in North j^merica, for the reason that 

 there is a greater diversity in the butterfly fauna of our country. All the 

 species that are now known as true parasites upon our butterflies are in- 

 cluded in the following lists. It will be noticed that they all, with one 

 exception, belong to the same genera as do the European species. Masi- 

 cera is sometimes difiicidt to distinguish from Tachina, in its narrowest 

 sense ; the three species described below, from the length of the third 

 antennal joint, I have no hesitation in referring to Masicera. As several 

 of the butterflies upon which some of the flies are parasitic are either cos- 

 mopolitan or introduced, it is not at all improbable that the parasites may, 

 in the future, be found to be identical. As everyone who has given any 

 attention to the Tachinidac is aware, the description of a species is insufl?- 

 cient to base a positive determination upon when the observed habitat is a 

 remote one, and nothing more than an opinion can be hazarded till an 

 actual and close comparison is made of specimens. Further, it is to be 

 borne in mind that the identity of the host is only of negative value in 



