Microdon. 581 



colour, the length is 11 mm. The pupa is similar to the larva, but 

 has two short anterior spiracular tubes; the pupa of Eggeri is 7 — 10 mm 

 long, with somewhat long anterior spiracular tubes ; the pupa of niuta- 

 hilis is 10 mm long, the anterior spiracular tubes are short. 



The larvæ live in the nests of ants; they have been recorded 

 from Forniica rufa L., F. fusca L. and var. fusco-riifibarhis F., F. san- 

 guinea Latr., F. exsecta Nyl., Lasius hrwmeus Latr., L. niger L., L. 

 flavus F., L. fuUginosus Latr., Camponotus herculeanus L. and C. ligni- 

 perda Latr.; there seems, hov^ever, according to Andries, to be some 

 reason to believe that the larva generally found with the various ants 

 (also F. fusca) belongs to M. Eggeri (or to species with a similar larva), 

 w^hile the larva of M. mutahilis is probably found only with F. fusca 

 and V. fusco-rufibarhis. Andries found always the larva of M. Eggeri 

 in stems and stubs of trees inhabited by ants, generally in stubs of 

 spruces and firs, more rarely in stubs of beeches and oaks ; the larva 

 of M. mutahilis (and rhenanus) she always found with F. fusca and 

 fusco-rufibarbis, and nearly always under stones, only in a single case 

 in a stub inhabited by F. fusca. Foreign species of Microdon have 

 likewise been found in nests of various ants (see Wheeler 1. c. and 

 Knab and Malloch [Trans. Roy. Soc. of South Australia XXXVI, 1912, 

 233], in which latter paper two Australian species are described 

 together with their puparia, found with ants); Wasmann mentions 

 (Krit. Verz. d. Myrm. und Termitophil. Anthrop. Berlin 1894, 175) Micro- 

 «?ow-larvæ from nests of Termites, but says that it is not certain, 

 whether the larvæ did not belong to ants living in the vicinity of the 

 nests of the Termites. — The pupa is found on the same piaces as 

 the larva. The larva hibernates, the pupation takes place between 

 the middle of April and the end of May. The puparium is opened 

 in a special way, differing from other Syrphids, as three pieces are 

 detached, while in other Syrphids only two. The pupal stage lasts, 

 according to Andries, as an average 18 days (in all from 15 — 23 days). 

 The eggs are deposited in slits in the bark; Andries found them at 

 the end of May and in the beginning of June, and she gives interesting 

 remarks about the egg-deposition, which she observed as the females, 

 she held in captivity, deposited. The egg of M. Eggeri is white, oval, 

 0,7 mm long, 0,3 mm broad; the shell is beautifully ornamented. On 

 an average there were twelve days between the deposition and the 

 escape of the young larva. The reason why the Microdon larvæ live 

 in the nests of ants, and what they feed on are questions not yet 

 solved; Wheeler (1. c.) suggests that they take the minute pellets of 

 food, which, after their moisture has been extracted, are rejected from 

 the hypopharyngeal pockets of the worker ants. 



