Last year during a Tanyptera Project recording day on the Hightown dunes between Formby and Crosby I caught a bristly black fly which on examination under the microscope turned out to be a species new to Britain, Phorbia penicillaris in family Anthomyiidae. This was a solitary male with tattered wings, and one could only speculate as to whether it had arrived after a long journey from continental Europe where it is known from sandy habitats both at the coast and inland or was a stray or long-lived member of a native population.

NW Invertebrates blog post on the original discovery

This find has been reviewed and published in Dipterists Digest Vol 32 No 2, pp149-151.

On fine sunny weather on 23 April I returned to Hightown with my sweep-net and spent a couple of hours in the same 800m stretch of dunes. There were indeed many black bristly flies to be found, though I still thought it unlikely that any of them would be P. penicillaris. How wrong I was! It transpired that I had collected 71 specimens – 40 male and 31 female. 

We know that flies in this genus lay eggs in slits in grass stems, made with their machete-like ovipositor.  This is just visible in the photo below by Jindřich Roháček from a publication on Diptera of sand-pits in the Czech Republic.

This raises lots of further questions, of course. Why has this species not been recorded in Britain before?  Is this a unique colony, or are there others elsewhere on the Lancashire coast or elsewhere in Britain?   The latter is certainly possible given the early date of emergence in the year and the few recorders of Anthomyiidae. It seems more likely that this colony is a relict from the original formation of the British fauna after the last ice age, than that there has been a more recent colonisation. Perhaps keen-eyed photographers will be able to find it with the help of this photos – it’s the size of a house-fly or bluebottle, up to 8mm in length.