The picture winged fly Dorycera graminum (F.) (Diptera, Ulidiidae) in abundance
at a threatened site in West Thurrock, with records from other sites in South Essex
PETER HARVEY
32 Lodge Lane, Grays, Essex RM16 2YP email: grays@peterharvey.freeserve.co.uk
Dorycera graminum is a medium sized and distinctive fly with marked wings (see inset plate 7),
which was given Red Data Book Category 3 (Rare) status by Falk (1991). It was subsequently
thought that the species had declined and might be reduced to only one or two dry grassland sites
(Stubbs 1997). It was therefore included in the Biodiversity "Long List" (Anon 1996) and is included
in English Nature's Species Recovery Program.
Evidence has been accumulating that an important metapopulation of the fly is present in the highly
threatened East Thames Corridor region of southern England. Many of the sites and habitats where
the fly has been recorded are either already destroyed by development, or under enormous threat
from the development pressures of the 'Thames Gateway' and initiatives such as the Thames Chase
Community Forest (Harvey 2000). Dorycera is threatened along with other nationally rare and
scarce grassland invertebrate species occurring in the same region, including national Biodiversity
Action Plan species such as the aculeate Hymenoptera Shrill Carder Bec Bombus sylvarum, the
'Brown banded' Carder bee Bombus humilis and the solitary wasp Cerceris quinquefasciata.
Dorycera graminum has been found on a number of occasions in the Chafford Hundred development
area in Grays Thurrock (TQ57/TQ67) between 1995 and 1999 (Ismay 2000) and the species has
also been recorded at several other south Essex locations since 1996 (D.A. Smith, pers.comm.).
The author first found the species at Vange Heights (TQ7187) on 31st May 2000, when a single
female was swept from tall open flower-rich grassland on a south facing clay slope. On 24th May
2001 one was caught using a sweep net in a sparsely vegetated area within tall un managed grassland
at the edge of Blackshots Nature Area (TQ6280) and subsequently four more were swept from
nearby yellow Crucifer flowers Barbarea sp. On 29th June 2001 a single Dorycera graminum was
beaten off a group of young pines in an open grassland area at Shoebury (TQ9384), but it escaped
and could not be refound. A week later, on 6th July 2001, a single somewhat battered specimen was
again beaten off pine at the same location, just possibly the same individual. On 31th May 2002 a
single female was beaten off scrub edge by the side of a footpath on sands and gravels above the
eastern side of the Ingrebourne Marsh near Rainham (TQ537839). To the eastern side of the footpath
there are old silt lagoons containing areas of flower-rich grassland as well as scrub and developing
woodland. Subsequently the species was swept in some numbers on 12th June 2002 at several
locations on the western side of the Ingrebourne Valley in the nearby Hornchurch Country Park
(TQ5384) from Hogweed Heracleum sphondylium flowers growing at the edge of flower-rich
grassland on the side of a young pine plantation and in rough grassland. Three males and seven
females were collected.
The most remarkable locality though was Anchor Field (TQ591779) (see plates 7 and 8) adjacent
to Lakeside in south Essex near the M25. The site was visited on 16th May 2002 with the purpose of
investigating its invertebrate fauna. Male and female Dorycera graminum were swept in some
numbers (up to half a dozen individuals per sweep) from open grassland vegetation, as well as at
the base of hawthorn and elm scrub. Hundreds of males and females were present on Hoary Cress
Cardaria draba, flowers where these were growing in large masses at the northern end of the field,
76
Essex Naturalist (New Series) 19 (2002)