Notes on the Early Stages of the Syrphid 

 Genus Microdon (Diptera) 



By Frank R. Cole, Stanford University 



The peculiar larvae of the Syrphid flies of the genus Microdon 

 have been described by several entomologists, but they are known 

 in only a few species. Enthusiasts in past years placed these 

 bizarre forms among the molluscs in two or three instances, and 

 one entomologist stated that they were the early stages of a Coccid 

 on oaks. Wheeler has given a very interesting account of some 

 of these early stages and the habits of the flies. In America the 

 larvae are recorded only from ants nests, but Wasmann states that 

 they may be found in the nests of certain wasps and termites. 

 They live in nests in the soil, under rocks or under the bark of 

 old logs. 



The larvae creep very slowly, with a wave-like motion of the 

 flat ventral sole, which is fringed and applied closely to the sur- 

 face over which they are travelling. Their food is probably, as 

 Wheeler believes, the minute pellets of food ejected from the 

 hypopharyngeal pockets of worker ants after the moisture has been 

 extracted. There is evidently one brood in a year, the flies emerg- 

 ing in May and June. 



In May, 1917, the writer found a number of pupae of Micro- 

 don cothurnatus Bigot, while collecting in the Hood River Valley 

 of Oregon. The type of this species came from "Mt. Hood," prob- 

 ably somewhere in the valley north of the mountain. While pull- 

 ing off the bark from an old pine log an ant's nest was uncovered, 

 and among the frenzied inhabitants of the nest a number of 

 Microdoyi pupae were noticed. The ant was later determined as a 

 subspecies of Camponotus maculatus. At this date. May 19, there 

 were no larvae of the fly present and the pupae were all fully 

 developed. Eighteen pupae were taken, most of them rather closely 

 crowded near the entrance to the nest ; all around them were empty 

 puparia, bearing evidence that the nest had been used for several 

 seasons by the flies. There were several adult flies around the log, 

 some of them freshly emerged, but the ants were so aroused at the 

 disturbing of their domestic tranquility that they quickly drove out 

 any strange insect that came near. The puparia taken were allowed 

 to become too dry and only two adults emerged out of the lot. 



In April, 1921, some observations were made on another 

 species of Microdon. A student at Stanford University, Mr. Her- 

 bert Mason, found a single larva in a nest of Camponotus maculatus 

 vicinus Mayr. This specimen was reared by Mr. Carl Duncan and 

 the specimen and notes regarding it kindly turned over to the 

 writer. The species proved to be Microdon piperi Knab, a beautiful 

 dark blue species which ranges north along the Pacific coast region. 



The larva was not closely examined by the writer, but in the 

 notes made on the specimien the color was given as largely pale 



