On 12th July 2017 I took 2 male and 2 female Dolichopodidae flies in Newton Beck Valley, a small wood on the edge of Lancaster. Unable to determine their genus, never mind species, I put them aside until more recently when I came back to them… but still without success. Having an opportunity to show one to Martin Drake (of the Empidid & Dolichopodid Recording Scheme) he identified it as the non-native species, Micropygus vagans, which was first found in Britain in 1995, in southwest Scotland.
The genus Micropygus is endemic to New Zealand with 16 recorded species there although now, in Europe, M. vagans has been found in Ireland and Britain. It is a small fly with body about 2mm and a general description, with figures, is given in Chandler (1999). The E&D Newsletter No. 19 gives some more up-to-date information.
Looking at its distribution map it appears to be expanding its range in Scotland but also moving south into England. This Lancaster record brings it into VC60 and is the southernmost record reported so far. It is certainly worth looking out for in the northwest and its distinctive character of an unpigmented outer crossvein is a good indicator amongst other small Dolichopodids.
My thanks to Martin Drake for the identification and for current information on its distribution.
References [freely available online]
Chandler, P.J. 1999. Micropygus vagans Parent (Diptera: Dolichopodidae), a New Zealand fly in the British Isles. British Journal of Entomology and Natural History 12, 215-220 (standalone article below)
Empidid & Dolichopodid Recording Scheme Newsletter No. 19, Autumn 2014