( 221 ) 
ON A SPECIES OF MICRODON FLY (DIPTERA) FROM 
NATAL. 
By S. H. Skaife, MA., M.Sc. 
(With Plate XIII.) 
The genus Microdon (Syrphidae) is remarkable for the aberrant nature 
of the habits and structure of the larvae. The majority of the species 
included in this genus are rare nnd little known, and in the ease of only 
very few of these species are the larval, pupal and adult forms known. 
The larvae, in the few cases known, are tolerated guests, or synoeketes, of 
ants, and are mollusc-like creatures, more or less hemispherical in shape, 
and move slowly along on the flattened ventral surface. Their relationship 
to their hosts has never been ascertained, but it seems probable that they 
are scavengers, like the larvae of the nearly allied genus Vohicella. 
Bezzi, in his Syrphidae of the Ethiopian Region (1915), lists twenty 
species of Microdon from Africa, and of these some half a dozen are recorded 
from South Africa. He provisionally subdivides the genus into six groups, 
and the species described in this paper comprises his Group I. In Bezzi's 
work this subdivision includes only the one species, M. iUucens, Bezzi, from 
Mozambique, a species which was founded on a single badly mutilated 
specimen. Nothing was known of the immature stages when Bezzi published 
his description. The present paper consists of a description of these stages 
together with a complete description of the adult. 
A nearly full-grown larva was found on March 3, 1920, in an old bag of 
AcantJiopsyche junodi, Heylaerts, at Mountain Rise, near Pietermaritzburg. 
The bag had been long vacated by its original owner, and was occupied, 
when found, by a small colony of the little black Doliclioderine ant, 
TecJinomyrmex albi^Jes, Smith, race Foreli, Emery,* the Microdon larva 
being a guest of these ants. The ants and their guest were placed in a 
small Petri dish, together with a little honey and water to serve as food for 
the ants. The larva moved slowly about the nest and seemed to be totally 
ignored by its hosts. It apparently took no food, and there was very little 
refuse present on which it could feed. At the end of ten days it ceased 
moving about and its skin darkened somewhat in colour. On March 16, 1920, 
two small, chitinous horns were seen to be protruding from the anterior 
portion of the larva's body, thus marking the commencement of the pupal 
stage. On April 8, 1 920, the adult emerged, after a pupal stage of twenty- 
three days. 
Descri])tion : Microdon illucens, Bezzi. 
Larva. — 5-6 mm. long x 3-5-4 mm. broad. Yellowish wdiite in colour; 
* Determined by Dr. G. Arnold. 
