12 BRI T I SH B LOOD- SUCKING F L I E S NEMA TOC E R A—CUL I C I DA E 13
A'édes detritus Haliday
(Plate 7)
Al though included among the dark- legged species of the genus Aëdes,
A. detriUis has in fact rather pale legs, owing to the more or less copious
sprinkl ing of white scales among the black ones, except towards the tips of
the tarsi ; there is usually also a considerable sprinkling of white scales on the
dark part s of the abdomen and on the wings. Thi s " pepper-and-salt "
appe a r anc e is usually a sufficient indication of the identity of the species. The
thorax is uniformly brown, without the dark median stripe characteristic of
A. punctor ; the pale bands of the abdomen are usually of even width.
A. detritus is a very abundant species on all the low-lying coasts of Britain.
It may extend some distance up our estuaries, but is not found far f rom tidal
water except in the brine district of Worcestershire.* Adul t s have been collected
in every month of the year, though they are most abundant in summer .
The e g g s of A. detritus are deposited amids t the vegetation of coastal
mar shes ; they are able to retain their vitality for at least a year (probably
much longer), whether dry or submerged, and some of them hatch on each
successive occasion that the mar shes are flooded by an exceptionally high tide
either directly or by water percolating through a sea-wall. Hence, in areas
which are subject to alternate flooding and drying, fresh stocks of larvae are
periodically produced, the greatest number s after the highest tides. The larvae
are able to s tand a very high degree of salinity (very much greater than that of
sea-water), with the important result that mosqui to production in coastal
districts is able to continue unchecked through periods of drought. Ap a r t
f rom the fact that all the eggs do not hatch at once, it is almost certain that in
A. detritus several complete life-cycles may be pas sed through during the year,
and in hot weather the period required for one of these cycles may be as short
as a fortnight.
Females of A. detritus are vicious and persistent biters, and have been
ascertained to have a flight-range of at least four miles ; the species is therefore
a source of widespread and serious annoyance in coastal districts.
Aèdes leucomelas Meigen
Thi s is very similar to A. detritus, but lacks the sprinkling of pale scales on
the dark part s of the abdomen. It has only once been found in Britain, at
AVidmerpool, Notts., in Ma y 1919.
A. leucomelas is common on the coasts of Germany and Denma rk, and also
in central Europe. The larvae occur mainly if not solely in brackish water.
Aèdes caspius Pallas
(Plate 6)
The bright fawn-coloured thorax, with two rather narrow white stripes
running its whole length, is highly characteristic of this species ; in addition it
* Since this was written the species has been found on Wood Walton Fen, Hunts.
may be distinguished f rom all other British Aedes except A. dor satis by the
markings of the legs, the hind tarsi having pale cream-coloured rings embr a c ing
the joints, with the last segment entirely cream-coloured. The scales of the
head are mostly bright fawn-coloured like those of the thorax, with a conspicuous
white spot in front ; the abdomen of the female is dark brown above, with a
median yellowish stripe, transverse yellowish bands across the junctions of the
segments, and with lateral white spots ; the wings have a copious sprinkl ing
of pale scales among the dark ones. Var iat ions f rom this typical ornament are
frequent ; the white stripes of the thorax may be very narrow or absent, the
general tint of the thorax may be lighter or darker, and the yellowish scales of
the abdomen may be more numerous or the median stripe interrupted.
A. caspius is in the main a coastal insect, commonly associated with A.
detritus, and occurring with that species on all the low-lying coasts of Eng l and
and Wales, and also inland in the neighbourhood of Droitwich ; unlike A.
detritus, however, it extends up the Thame s estuary as far as London, and in
some seasons is abundant in some of the London suburbs . Adul t s have been
collected in April, June and July, but are commoner in Au g u s t and Sept ember .
The life-history of A. caspius is in general similar to that of A. detritus, the
larvae occurring together in salt mar shes and several broods being produced
during the summer . However, A. caspius differs f rom A. detritus in two
noteworthy respects : in the first place it is not confined to salt or bracki sh
water, having been found breeding on several occasions in fresh-water pool s
on commons near London and also in sewage beds ; secondly, the winter appea r s
to be pas sed exclusively in the e g g s tage, the first larvae appe a r ing in Apr i l .
As is the case with A. detritus, the females certainly fly for considerable
distances (at least several miles) f rom their breeding places, though not so f a r
as was formerly supposed.
A. caspius shares with A. detritus the responsibility for caus ing widespread
annoyance in Engl i sh coastal districts, being apparent ly more abundant than
its associate on the Ea s t coast, but less so on the south coast. It is also ext remely
troublesome in some seasons in the southern suburbs of London, somet imes
entering houses to bite.
Aedes dorsalis Meigen
In leg-markings and some other respects this resembles A. caspius, but the
two are very easily separated if their scaly vestiture has not been denuded. In
A. dorsalis the thorax has a broad dark brown median stripe and da rk brown
areas on each side, separated f rom the median stripe by broad areas of ashywhite
scales ; the median stripe and transverse bands of the abdomen are white
mstead of yellowish and the dark scales almos t black ; also the wings are less
evenly sprmkled with pale scales, some of the veins being almost entirely da rk.
A. dorsahs, like A. detritus, is in Britain a purely coastal species, but so far
It has not been found in many localities, these being in the counties of Dor set ,
Es sex, Norfolk, Wes tmor land, and the Isle of Ma n (Rams ey) . On the heaths
around Poole Ha rbour it has been recorded as biting fiercely.