SOME DIPTERA (MTCRODON) FROM NESTS OF ANTS. 



By T. D. a. Cookerell and Hazel Andrews. 

 Of the Vniverait)/ of Colorado, Boulder. 



An excellent summary of our Imowledge of the biolog}" of the 

 syrphid genus Mkrodon has been given by Dr. W. M. Wheeler/ while 

 the taxonomy of the North American species has been fully discussed 

 by Dr. S. W. Williston.^ A new species from Colorado was reported by 

 Cockerell many years ago,^ but was not described. W. A. Snow^ de- 

 scribed a new species from the male as Microdon meg alog aster; in the 

 Aldrich catalogue this is said to be from Colorado, but no locality is 

 cited b}^ Snow, and evidently he did not know where the specimen 

 came from. Snow's paper is mainly on Syrphidae from Colorado, but 

 he says in his prefatory note that the material discussed is "chiefly " 

 from the Colorado collection, implying that part of it is from another 

 source. Doubt is also thrown upon the locality " Colorado " by the 

 fact that Townsend described as M. hombiformis what appears to be 

 the female of the same species from Virginia, while Johnson reports 

 the species from New Jersey and Pennsylvania. It may be stated that 

 a specimen from Pecos, New Mexico (W. P. Cockerell), was referred 

 to Snow's species by Coquillett ; this is in the United States National 

 Museum, and Mr. Knab informs us that it is a female of our M. 

 coloradensis. Wheeler gives good reasons for thinking that all the 

 records of the breeding of Microdon in the United States refer to a 

 single species, M. tristis Loew. The junior author of this paper 

 was fortunate in breeding two species from larvae found in nests of 

 Formica in Colorado in the spring of 1915. Upon examination, it 

 seems that one of these is undescribed while the exact position of the 

 other seems somewhat uncertain, so they are characterized herewith. 



MICRODON COLORADENSIS, new species. 



Male. — Robust; length (not including antennae), 14 mm.; width 

 of abdomen about 6.7.5 mm.; length of wing 9.0 mm. Head black, 



Proceedings U. S. National Museum, Vol. 51— No. 2141. 



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