Download - NERC Open Research Archive - Natural Environment ...

Leucorrhinia dubia (Vander Linden) White-faced dragonfly
Description L. dubia is a small dark libellulid which derives its name from its pale creamy white
frons, clearly visible from the front in flight at close quarters. Sympetrum danae is
also small and dark, but it lacks the white frons and the dark basal wing patches of
L. dubia. In mature male L. dubia, the narrow abdomen is black with red markings
on the dorsal and lateral surfaces of segments 2 and 3, reddish spots mid-dorsally
on segments 4 and 5, and larger orange spots mid-dorsally on segments 6 and 7.
These may become redder with age. The wings have dark black-brown patches
basally, which are less extensive on the forewings, and red coloration mid-dorsally
on and between the wing attachments. The thorax is black with faint red
antehumeral stripes and lateral markings. In immature males and in females, the
red and orange markings of mature males are pale creamy yellow
Habitat L. dubia breeds in acidic and usually oligotrophic bog pools which contain an
abundance of submerged Sphagnum moss. Occasionally, on cut-over bogs, larvae
will emerge from peat-stained pools with negligible amounts of submerged
vegetation, but invariably these are at sites where Sphagnum-dominated pools are
in close proximity. At some lowland sites, the submerged moss Drepanocladus
fluitans is also plentiful. At several basin mire sites in the English midlands, the
pools, up to 14 m deep, may have been formed as a result of the collapse of a
schwingmoor. L. dubia is confined to waters with no fish (Henrickson 1988).
Breeding biology L. dubia is territorial but its territories are not large. Interaction between L. dubia
and Libellula quadnMaculata is discussed by Warren (1964), and is referred to
more fully in the account of the latter species in this Atlas. Copulation takes place
amongst low bushes or heather and is of short duration. The female oviposits by
flying low over the bog pool, usually unaccompanied by the male, and dropping
her eggs into the water or on to water-logged Sphagnum moss. The larvae, which
live amongst submerged Sphagnum, usually take two years to develop.
Flight periods L. dubia is on the wing from late May to the end of July. It may be seen with other
species such as Sympetrum danae, Aeshna juncea, Pyrrhosoma nymphula and
Lestes sponsa.
Status and distribution The first authenticated record of L. dubia in Britain was at Thorne Moors, Yorkshire,
on 28 July 1837 by William Beckitt, who passed a specimen to J C Dale (Lucas
1908; Limbert 1985). The species has a very disjunct distribution in Britain from
Surrey to north Scotland. It has not been recorded from Ireland. Its strongholds
are in Inverness-shire and Ross-shire. It appears to have declined in Perthshire
and Argyllshire, not having been reported since 1972. L. dubia has declined
notably in England over the past 35 years, having been lost from six sites between
1956 and 1976. Only seven breeding sites remain. Its sole Welsh locality, Fenn's
and Whixall Moss, is at a site which straddles the border with England. The
decline of L. dubia in Britain is due principally to the loss of habitat, caused by
drainage associated with afforestation, commercial peat cutting and agricultural
reclamation. Seral changes, which result in the drying out of the habitat and its
encroachment by scrub and trees, are a danger at bogs which have already been
damaged by human activity, and are most marked at the sites of former small-scale
peat diggings (Key 1989; Eversham 1991). One site, in Surrey was probably lost
as a result of drying out in the drought of 1976. L. dubia occurs within several
NNRs and anRSPB reserve. The appearance of L. dubia at an atypical, locally wellknown
site at Stone Edge, Derbyshire, in 1987-89 is now thought to have been an
abortive attempt at introduction. L. dubia was reported from at an atypical site at
Walberswick NNR, Suffolk, in 1992 (Mendel 1992); none was seen there in 1993 or
1994.
European and world L. dubia is found throughout northern Europe, and east to Siberia. At the southerly
distribution limits of its range it is restricted to mountain areas such as the Pyrenees and Alps.
108