Hesse (1969) described this species as follows: Body with the abdomen rather broadish; colour mainly or almost entirely dark or black, though the vertex and frons on each side, clypeus, proboscis below, humeral tubercles, postalar calli, pleural parts, and sometimes the abdomen above, and usually base of venter, reddish brownish or piceous brownish to a variable extent, occasionally body may be mainly brownish or piceous brownish; antennae usually dark reddish brownish, the clubs usually orange-yellowish towards apices or in apical halves, or sometimes entirely so; an infusion on thorax anteriorly on inner side of humeral tubercles, extending backwards to a variable extent as a submedial streak more consistently yellowish or reddish, and in pale specimens sides of thorax similarly coloured; hind margin of tergite 1 usually reddish brownish and in specimens with more piceous or brownish abdomen hind borders of tergites are dark or black ; bullae variable, dark reddish brownish to orange yellowish, black margined, usually smallish and widely separated; legs brownish to reddish brownish, more yellowish in more brownish specimens, the apices of femora above, especially hind ones, darkened, and the tibiae, especially front and middle ones and tarsi, usually paler, more yellowish. Integument of middle parts of frons, clypeus, pleural parts, coxae and abdomen shining; that of tergites-3 and 4 on sides and more so on 5-8 discally transversely 'nadelrissig', becoming coarser and denser, more striate on last two segments, especially last one ; integument of disc of thorax above dull, but unlike that of A. callosus and other species of Arenomydas, not rugulose, but unsculptured dull, the metanotum however more transversely rugulose. Vestiture poorly and sparsely developed, that on head short and sparse, except on head below and in occipital hollow; shortish and sparse ones on head in front yellowish to brownish, the longish, somewhat sparse ones on head below and those on head behind, and sparse ones on propleural tubercles, greyish whitish; shortish, decumbent hairs on sides of thorax above and in discal streaks fulvous brownish; fine, short, scarcely perceptible ones on pleurae and on sides of tergite-1 also yellowish brownish; abdomen above with scarcely any short hairs, but more distinct reversed ones on last two segments also fulvous brownish; hairs on legs fulvous brownish, short and sparse, more so on coxae, and those on tibiae longer and denser, especially along inner lower parts; spines and spicules on legs fulvous to fulvous reddish. Head with the antennae usually shorter, or much shorter, than thorax; segment-1 short, about 2–2.5 times length of 2; segment-3 slightly, but distinctly, thickened apically; club elongate, subspindle-shaped, narrowed apically and constricted at base, much longer than segment-3; proboscis shortish, its labella relatively small, the proboscis either slightly shorter than, as long as, or slightly longer than, vertical length of eye; palps distinct, a little longer than antennal segment 2, golden-haired. Wings tinted greyish yellowish to faintly brownish, more brownish along veins, especially in anterior half, the apex and hinder half clearer; veins yellowish brownish; first posterior cell rather arched outwards; base of second submarginal cell tending to be more consistently acute or angular; apex of discoidal cell shortly stalked; squamal margin yellowish brownish to brownish; halteres dark brownish to almost black. Legs with the hind femora slightly thickened, armed with a double row of spines below from just before, or at about, the middle and invariably with some (2-5) distinct spines on outer apical aspect ; tibiae curved, and hind ones armed with rather numerous, longish and conspicuous spicules along outer and lower parts (as in callosus), the apical ones rather long and bristle-like; tarsi rather shortish, the basal segment of hind ones distinctly longer than claw-segment. Oviscape with 8–11 slender, fulvous spines on a side. Length of body: about 10-12 mm; Length of wing: about 8-10 mm.

This is a smallish, rather plump, dark species belonging to the A. callosus section (Hesse 1969).

Type locality: South Africa, Western Cape, between Leipoldtville and Elands Bay.

Arenomydas is southern African endemic genus with about 9 described species, with one record from southern Namibia (Kirk-Spriggs and Sinclair 2017).

South Africa.

South Africa, Western Cape between Leipoldtville and Elands Bay (Museum Expedition, Oct. 1947) (holotype and paratypes).

The information below was extracted from Cannings and Scudder (2005): Dipterans are primarily aerial insects and the mesothorax, which bears the only pair of wings, dominates the thorax - the prothorax and metathorax are greatly reduced. The legs are normally rather simple and are used primarily for perching; in some groups, they are modified for prey capture or for signaling during courtship. The tarsi are nearly always 5-segmented. The functional wings are membranous and their pattern of veins is critical in fly classification and identification. During the evolution of flies, there has been a trend towards a reduction in veins, especially in the rear half of the wing – changes that evidently relate to improvements in two-winged flight. The hindwings, present in most other insects, are reduced in Diptera to small, club-like organs, called halteres, used for stabilising flight.

Herbivore - Nectarivore (nectar-eating)

This species visits flowers and most of the specimens were taken on the flowers of the Hottentot's fig (Carpobrotus edulis) and the sour fig (Carpobrotus acinaciformis) (Hesse 1969).

Like the others, flies in the Mydidae family begin life as an egg, which hatches into a grub-like larva. Most of the fly life is spent in the larval stage, mainly eating and growing as well as molting several times. Some flies may spend at least a year as a larva. The next stage is a pupa, during which the insect transforms into its final stage, emerging from the pupa as a winged adult, able to mate and reproduce. In many species, males stake out positions at favourable egg-laying sites and wait for females to arrive (Hesse 1969).

Specimens have been collected from September - November (very few records for August and December) (Kirk-Spriggs and Sinclair 2017).

Fynbos.