A couple of days ago I received an interesting parcel from Chris Bentley, the warden of Rye Harbour NR. Chris is a keen Dipterist and had turned up some fantastic records in the past – namely the Brown-tail parasitoid Townsendielomyia nidicola and the extremely rare Huebneria affinis – so I always look forward to receiving something from him. He had pre-warned me that he had some suspected Erynnia ocypterata and some Carcelia that he couldn’t quite place and suspected atricosta, which is one of the rarest species in that genus (gnava and laxifrons possibly being slightly rarer species).
Anyway, the Erynnia ocypterata were fairly easy to identify and confirm … this is an incredibly rare species in the UK, with only a handful of post-1950 records (Mike Howe & Ivan Perry). Chris’s specimens were seen “buzzing round a gatepost below a large willow … on grazing marsh with ditches” in the Rye area of Sussex.
The Carcelia were a little bit fiddly because they’re not the easiest genus to identify – the species are quite clear-cut but you do have to be able to measure the frons-width with a graticule to be quite sure, and male genitalia are very useful so these must be extracted during the pinning process (as with all calyptrates really). In these there had been some damage/flattening to the bristles on tergite-4, which had confused Chris and sent him the wrong way. On close examination they actually proceeded fairly easily to Carcelia laxifrons and the frons/genitalia backed up the ID nicely.
Carcelia laxifrons is a specialist parasitoid of Brown-tail moth (Euproctis chrysorrhoea) and, as such, it’s distribution is restricted to areas with a good concentration of the host (one might expect southern counties, especially coastal areas). In fact the species has only been recorded from the Rye area and a few other sites and was so overlooked that it was only added to the British list a few years ago – see “Carcelia laxifrons Villeneuve (Tachinidae) new to Britain and a revised key to the British Carcelia species” (Raper, Smith & Gibbs, 2004).
Many thanks to Chris who donated the specimens and filled 2 important gaps in my reference collection and to Malcolm Storey (http://www.bioimages.org.uk/) who did the photo stacks! 🙂