206 



Journal New York Entomological Society. [Vol. xvi. 



puparia from which the flies must have escaped during the previous 

 spring. The ants resented my interference by moving to a new nest. 

 On July 25 I found two more partly grown larvae in the deserted for- 

 micary, but these were weak and emaciated. This shows that the 

 Micrddons do not accompany the ants when they move, and that the 

 presence of the latter is essential to the well-being of the former. The 

 emaciated condition of the abandoned larvae is easily accounted for, 

 if they feed, as I believe they must, on the ejected hypopharyngeal 

 castings of their hosts. 



The larva of M. tristis (Fig. 1 ) is 8-10 mm. long, opaque, pale, 

 dirty brown or dark drab above and lighter beneath. The border is 

 brown and striated and bears a simple fringe of short, flattened and 

 pointed hair-like processes. The convex dorsal surface is covered with 

 a coarse reticulum consisting of pale gray, cord-like elevations, which 

 converge toward the anterior end and the posterior tubercle. On 

 closer examination the convex surface is seen to be divided into five 



subequal areas by four longitudinal strips 

 which are rather free from reticulations. 

 The posterior tubercle is short, robust, 

 rounded, opaque, yellow, and covered with 

 minute papillae of the same color as the re- 

 ticulum on the dorsal surface. This tubercle 

 is surmounted by the two reniform anal stig- 

 mata, which are sometimes connected by a 

 bridge. They are dark brown and shining. 

 The puparium is of the same size as the 

 adult larvae, but more convex and dark 

 brown in color. Its sculpture is like that 

 of the larva, but there are two prothoracic 

 tubercles, each less than twice as long as 

 broad, slightly diverging and somewhat 

 obliquely truncated at their tips, which are 

 shining and covered with minute papillae. 



The following additional observations on tristis were made during 

 the past spring. April 19 I found a flourishing colony of F. schaufussi 

 under a large flat stone in a sloping pasture at Bronxville, N. Y. The 

 nest contained twelve adult larvae and twelve puparia of tristis, all 

 attached to the smooth earthen walls of the galleries either at their 

 entrances or not more than 3 cm. below the surface of the soil. In 



Fig. I. — Larval Microdon 

 tristis Loew ; dorsal aspect. 

 X6. 



