Part 2: Nematocera and Aschiza not dealt with by Falk (1991) - JNCC

as semiaquatic plants, rocks and leaves, where they are filter
feeders. Adults recorded from January to March and from
May to October.
Status There are more than 20 known post 1960 sites, in
Devon, Somerset, Leicestershire, Cheshire, Yorkshire and
Cumberland as well as Breconshire in Wales. Status revised
from RDB 3 (Shirt 1987).
Threats The canalization and clearance of vegetation from
stony woodland streams; pollution such as agricultural
runoff and eutrophication.
Management and conservation Maintain stony woodland
streams in a natural state, free of excessive disturbance.
Published sources Brindle (1962); Disney (1975, 1999);
Emley (1992); Gibbs (2002); Goldie-Smith (1990); Kidd &
Brindle (1959); Peach & Fowler (1985).
DIXELLA FILICORNIS
A meniscus midge LOWER RISK (Nationally Scarce)
Order DIPTERA
Family DIXIDAE
Dixella filicornis (Edwards, 1926)
Identification Keyed by Disney (1975, 1999).
Distribution A scattered distribution, with sites throughout
England (Cornwall, Devon, Hampshire, Sussex, Kent,
Norfolk, Cambridgeshire, Gloucestershire, Staffordshire,
Leicestershire, Cheshire, Westmorland), and a few sites in
Wales (Cardiganshire, Merionethshire) and Scotland
(Perthshire, Angus). There is a confirmed record from
Angley Wood, Cranbrook (1987) in West Kent but a record
from Oare, Faversham (1988) requires confirmation in the
light of the discovery of D. graeca (Pandazis).
Habitat Swamps with rushes and other emergent vegetation
at margins of eutrophic lakes fringed with trees and
hydrosere sedge swamp in woodland; also streams and
pools on wet heathland. It is said that this species prefers
shaded areas although this is clearly not always the case,
and fourth instar larvae have been found in an unshaded
shallow roadside ditch, attached to grass blades hanging into
the water from an overhanging and undercut ditch bank.
Ecology The aquatic larvae are found at the meniscus of
water bodies, especially against emergent structures such as
semiaquatic plants, where they are filter feeders. Adults
recorded in January to March and June to November.
Status About 20 widely scattered post 1960 sites. Status
revised from RDB 3 (Shirt 1987).
Threats The destruction of wetlands and swampy woodland
through drainage; mismanagement of water levels with a
loss of breeding sites; pollution such as agricultural runoff
and eutrophication of streams. Ditching and canalization of
streams and rivers is also detrimental.
Management and conservation Maintain a high, relatively
stable water level and a rich emergent marginal vegetation.
Use rotational ditch/pond management where necessary and
retain tree cover in swamp woodlands.
Published sources Disney (1975); Emley (1992); Fowler
(1984, 1987); Goldie-Smith (1990).
DIXELLA GRAECA
A meniscus midge
Order DIPTERA
Dixella graeca (Pandazis, 1937)
DATA DEFICIENT
Family DIXIDAE
Identification Characterised by Disney (1992) and keyed
(1999).
Distribution Records from three sites in England:
Mountsfield, Rye, East Sussex (first found as larvae 13 May
1988, E.K. Goldie-Smith); Walberswick, East Suffolk (14 to
29 August 1989, A. Foster & D. Procter); Chippenham Fen
NNR, Cambridgeshire (larva, 5 August 1991).
Habitat The Sussex site is a secluded undisturbed pond
surrounded by trees. In Suffolk it was a flooded unmanaged
dense reed swamp, while at Chippenham Fen NNR it was a
mixed woodland stream close to more open meadow.
Ecology All stages were subsequently studied at the Sussex
site, where marginal sedges and many fallen leaves were
available for oviposition. At Chippenham Fen NNR a single
larva was found in the woodland stream site. Larvae are
aquatic filter feeders at the water meniscus.
Status This is the smallest of the British Dixidae and may
have been overlooked and consequently under-recorded.
The original Sussex record was initially determined as D.
filicornis (Edwards) and another record assigned to the
latter from Oare, Faversham, Kent (1988) requires
confirmation. Subsequent visits to the latter site, which is
threatened by water management, have not resulted in fresh
material of either species being found. Currently there is
inadequate information to assess the risk of extinction. Not
included in Shirt (1987) and Falk (1991).
Threats Drainage of ponds and other wetlands for
agricultural improvement; pollution such as agricultural
runoff and eutrophication. Excessive management of sites,
resulting in changes in water level or loss of emergent
vegetation.
Management and conservation Maintain ponds and
streams with marginal emergent vegetation, undisturbed or
managed on rotation if this is found to be necessary.
Published sources Disney (1992, 1999); Goldie-Smith
(1992, 1993).
DIXELLA OBSCURA
A meniscus midge LOWER RISK (Nationally Scarce)
Order DIPTERA
Family DIXIDAE
Dixella obscura (Loew, 1849)
Identification Keyed by Disney (1975, 1999).
Distribution Recorded from sites in northern England
(Lancashire, Yorkshire, Cumberland), Wales (Newborough
Warren, Anglesey, 1962) and Scotland (Selkirkshire,
Roxburghshire, Elgin and Easterness).
Habitat Mainly calcareous wetlands, especially sedge beds
and the transition of fen vegetation to more acid conditions
(with bog bean Menyanthes and fen Sphagnum in evidence),
Alder (Alnus) swamps, marshes, ponds and streams.
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