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

Aeshna mixta Latreille Migrant hawker
Description A. mixta is a medium-size hawker dragonfly, similar in pattern and coloration
Habitat
to A. cyanea, A. juncea, and Brachytron pratense. In males, the antehumeral
stripes are much reduced or absent, thus separating A. mixta from the other
three species. The costa is dark brown, distinguishing it from A. juncea in
which it is bright yellow. The abdominal spots on the dorsal surface of
segments 9 and 10 are paired, not joined together to form two broad bands as
in A. cyanea. A. mixta is much smaller than both A. juncea and A. cyanea,
though it is of similar size to B. pratense. However, A. mixta lacks the very hairy
thorax of that species, and its pterostigmata are not as elongated, neither do
their flying seasons overlap. In female A. mixta, the body markings are similar
to those of the male, but the coloration is much duller and the abdominal spots
are a pale yellowish green. The anal appendages of the female are the longest
of all our resident aeshnids, excluding B. pratense, being more than the
combined length of abdominal segments 9 and 10.
A. mixta breeds in ponds and lakes, including flooded sand and gravel pits,
with well-vegetated margins. It also breeds in canals, ditches, which in coastal
areas may be quite brackish, and, occasionally, sluggish rivers and streams.
On heathlands, A. mixta appears to avoid the more acidic waters tolerated by
A. juncea.
Breeding biology A. mixta is usually only weakly territorial and occurs at higher densities than
larger aeshnids. It is not uncommon to see three or four males flying together
in a confined area without aggression. Even more than other Aeshna species,
A. mixta is frequently seen hawking at the edges of woods, along woodland
rides and glades, and beside tall hedges away from water, sometimes in large
numbers. Copulation time is lengthy and usually takes place in marginal
vegetation near the water's edge. Females insert their eggs into the tissues of
emergent plants, such as bulrush, often above water level, and will
occasionally oviposit into bare mud. Diapause is spent in the egg stage.
Larval development is rapid, being completed in one season.
Flight periods A. mixta has a late flying season, from late July to late October. It can be seen
Status and distribution
European and world
distribution
with many other late summer species, such as A. cyanea, A. grandis,
Sympetrum striolatum and the commoner damselflies.
A. mixta has not yet been recorded from Ireland. In Britain it breeds from
Cornwall and south Wales to the Humber, but is most common in southeastern
and midland counties. It has clearly extended its range in Britain
during this century Lucas (1900) wrote, 'This dragonfly seems to be almost
confined to the south-eastern corner of England and the Channel Islands, and
even from there but few captures have been recorded'. Longfield (1949c)
'reported that A. mixta was most commonly found in southern and eastern
' counties below the Severn/Wash line, and cites a few instances of its being
found further north. Benton (1988) records the spread of A. mixta into Essex in
:the 1930s and 1940s. In Bedfordshire, it was described in 1947 as being by no
means common, but it is now ubiquitous (Dawson 1988). Holland (1983)
records the spread of this species in Gloucestershire since the 1970s, as does
Allport (1985) in Yorkshire. In Cornwall, breeding was confirmed for the first
time in 1991. It was first recorded in Cheshire in 1993. The population of A.
mixta is sometimes increased greatly in late summer by influxes from the
continent. On 17 August 1982, in excess of a thousand were seen by K D
Wilson in a wood near Brighton, Sussex, many of which were teneral. Three
days later he found a similar number in a wood near Eastbourne, up to 25
settled on a single branch.
A. mixta is common throughout most of south and central Europe, being found
as far north as Denmark. It occurs in North Africa, the Caucasus, and east to
China and Japan.
68