Make sure your fly really is a tachinid and not a rhinophorid or sarcophagid – we have all made howling mistakes and it can be very embarrasing, not to mention a complete waste of time!
Tachinids (along with rhinophorids, sarcophagids, calliphorids, muscids and anthomyids) are calypterate flies and all calyptrates have the following features:
- a suture/groove that runs transversely across the top of the thorax, from a position just infront of the wing bases
- calyptrae/squamae, which are usually a pair of pale, rounded discs/flaps, just behind the wing bases and above the halteres. The front one is usually much smaller than the rear one.
Tachinids, rhinophorids, sarcophagids & calliphorids then split away from muscids & anthomyids because the former have:
- hypopleural bristles – a fan of hairs/bristlets in front and below (antero-ventral to) the hind thoracic spiracle.
Lastly, tachinids are split from the others by having:
- an enlarged subscutellum – when viewed from the side you should see a prominent, chitinous, smoothly rounded bulge below the rounded lip of the scutellum and above the next (much larger) bulge where the back of the thorax connects to the abdomen. Sarcophagids lack the subsculellum entirely and this is usually pretty obvious but don’t be fooled by the part of the thorax that connects to the abdomen. Rhinophorids are a little more difficult but they have a bulge that is not as large or rounded and is only partly chitinous – some also have very long petioles on the median wing-vein. A few rare tachinids (e.g. Cinochira, Litophasia & to a lesser degree, Catharosia) do not have a subscutellum but these are keyed out in the key to families usually or can be recognised visually because they are quite distinctive looking. I hope to have photos of these on the site soon!
The next things are ’gizz’ features – they are NOT stable, they are just generalisations that do not apply to all tachinids but are sometimes useful in the field:
- strong bend in wing-vein m – the middle wing-vein (m) usually bends with a pronounced angle before it meets the wing edge or joins one of the other wing veins.
- strong bristles – most tachinids have strong bristles over their entire body, not just hairs. A bristle has a socket at the base, whereas a hair just emerges from the integument.
- a delta-winged stance – when at rest tachinids often sit with their wings held in a delta shape – they are hardly ever held flat over their backs.