Tachinids that look like Eriothrix rufomaculata

Eriothrix rufomaculata is an incredibly common fly in mid-summer, especially on any flowery meadows. The species is very easy to identify from the red abdominal side-patches, silvery face with projecting mouth edge, long costal spine, slightly shaded wings with a small petiole on the median vein. The only problem is that several other, rarer, species can easily be confused for Eriothrix.

In this confusion group I will include: Mintho rufiventris, all Cylindromyia spp., Aphria longirostris & Bithia spreta. All of these confusion species have some nice clear features that you should be able to pick up in photos and I’ll bring those out below:

  • Two broad longitudinal black bars on the thorax and the abdomen laterally compressed (higher than it is wide, though this can be difficult to judge) but always wider nearest to the thorax, tapering to the tip and about as long as the head+thorax; strong median discal bristles present; wing with very short petiole. [if you have a fly with 2 dark bars on the thorax; longer, forward-pointing petiole; and long cylindrical body then suspect Cylindromya (below)] = Mintho rufiventris
  • Thin black longitudinal bars on the thorax numbering 2-4 but usually thin; abdomen various shapes:
    • Proboscis long, projecting forwards further than the antennae and extending beyond the face for at least as long as the depth of the head; median discal bristles absent; heavily pale-grey dusted = Aphria longirostris
    • Proboscis can project from the face a little but never as long as in Aphria
      • Abdomen cylindrical and longer than the head+thorax; median discals usually absent; wing with a forward-pointing petiole, longer than vein r-m = Cylindromyia
      • Abdomen normally-shaped and usually as long as the head+thorax; median discals always present:
        • Wing veins r1, r4+5 and cu all have little hairs along them; no petiole on the median vein; wings clear; basicosta pale; body heavily grey-brown dusted with faint orange abdominal side-patches = Bithia spreta
        • Wing veins bare with a tiny petiole, shorter than vein rm (can be as short as r4+5 and median vein touching at the wing edge); wings often slightly shaded; basicosta dark; body black with dark grey dusting and with red abdominal side-patches … but these can vary from occupying the whole length of the abdomen to almost absent = Eriothrix rufomaculata

Here are a few free-to-use images trawled from the web to illustrate some of the features described above: