2 BRITISH BLOOD-SUCKINCx FLIES
than one in which the species are first allocated to their respective natural
genera.
The species of the " domestic " group differ markedly not only in their
external appearance, but also in their " piping" When in flight. The female
A. niaculipennis in flight produces a note which varies in pitch from middle C
to E flat, according to whether the insect has fed or not ; that of T. annulata
varies similarly from A to B, and that of C. pipiens is a third higher (D').
In each case the note of the male is much higher than that of the female.
The family Culicidae includes two other small groups of gnat-like insects
in addition to the mosquitoes. As the species of these groups do not suck blood
they are not dealt with in this work, but those interested will find accounts of
them in papers by Edwards (1920, 1921, 1930), Martini (1929), and Peus (1934).
KEY FOR IDENTIFICATJON OF BRITISH MOSQUITOES.*
(Females only)
1. Palpi as long as proboscis ; abdomen without scales 2
Palpi much shorter than proboscis ; abdomen covered with scales 5
2. Wings spotted An. niaculipennis
Wings unspotted 3
3. Thorax uniform, brown ; head without frontal tuft An. algeriensis
Thorax darker at sides (as seen from above) ; head with frontal tuft of white scales 4
4. Body brown An claviger
Body black An. plwtibeus
5. Tarsi with pale rings (usually conspicuous, but may be narrow and rather faint) 6
Tarsi entirely dark ig
6. Wings with small dark spots ; large species 7
Wings without dark spots 9
7. Pale rings near tip of each femur and in middle of first tarsal segment of each leg 8
Such rings absent Th. alaskaensis
8. Abdomen with conspicuous white bands Th. a?inulata
Abdomen not distinctly banded, suffused with yellow Th. siibochrea
9. Tarsal rings spreading across the joints 10
Tarsal rings confined to the base of each segment 15
10. Black-and-white insect ; thorax with narrow sharply defined white lines . . O. pulchripalpis
Ornament otherwise 11
11. Abdomen with transverse pale bands only ; thorax without conspicuous ornament 12
Abdomen with median longitudinal pale stripe 14
12. Proboscis all dark Th. morsitans
Proboscis pale beneath in middle 13
13. Yellowish rings at all tarsal joints Th. futnipennis
Rings at last two tarsal joints of hind leg inconspicuous or absent Th. litorea
14. Thorax fawn-coloured with two narrow white lines Aid. caspius
Thorax with broad dark brown stripe, on each side of which is a broad ashy-white
^na. ^ dorsalis
15. First segment of hind tarsus with a pale ring in middle : wing-scales rather broad
Taen. richiardii
Such a ring absent ; wing-scales mostly narrow 16
16. Abdomen mainly yellow, unhanded Aed. flavescens
Abdomen distinctly banded 17
In using this key it must be remembered that the ornamentation of mosquitoes is due to a covering
of scales of different colours. When these scales are rubbed off (as very easily happens) the in-sect may
appear quite different, and identificaHon is not an easy matter.
NEMATOCERA—CULICIDAE 3
17. Thorax yellowish towards sides above Aêd. annulipes
Thorax darker 18
18. Pale bands of abdomen of uniform width Aëd. cantans
Pale bands of abdomen constricted in middle Aëd. vexans
19. Abdomen tapering ; claws toothed 20
Abdomen blunt ; claws simple 27
20. Abdomen unhanded 21
Abdomen with complete transverse pale bands 22
21. Thorax ornate, knees silvery 4ëd. geniculatus
Thorax dull reddish-brown, knees dark Aëd. cinereus
22. Abdomen with tendency to have a median longitudinal pale stripe, indicated at least
towards tip Aëd. rusticus
Abdomen without trace of such stripe 23
23. Abdominal bands (at least the last few) narrowed in middle, their posterior margins
/\-shaped Aëd. punctor
Abdominal bands not narrowed in middle 24
24. Fore and mid femora conspicuously sprinkled with pale scales in front 25
Fore and mid femora with only a few pale scales in front 26
25. Dark parts of abdomen with scattered pale scales Aëd. detritus
Dark parts of abdomen without scattered pale scales Aëd. leucomelas
26. Hind tibia with a white stripe on outer side Aëd. sticticus
Hind tibia without such stripe Aëd. communis
27. Pale bands of abdomen on anterior borders of segments C. pipiens and C. molestus
Pale bands of abdomen on posterior borders of segments C. apicalis
Genus ANOPHELES Meigen
The British mosquitoes of this genus may be distinguished (in the female
sex) from all those of other genera by several easily recognised peculiarities :
(i) the proboscis has a trifid appearance owing to the fact that the palpi
which lie on each side of it are of about the same length as the proboscis itself,
whereas in all the other genera of mosquitoes they are much shorter ; (2) the
abdomen is devoid of scales, and so lacks any definite ornament, such as white
bands or spots, whereas in all the other genera the abdomen is completely
clothed with scales which form a more or less conspicuous ornament ; (3) the
legs are of almost hair-like slenderness, besides being all dark ; (4) the insects
rest with the body at an angle with the surface.
In the early stages there are equally striking features in which Anopheles
differs from other mosquitoes. The eggs are always laid on the surface of
water, on which they float during the short period which elapses before the
hatching of the larvae ; they are deposited singly, not in boat-shaped masses
as in Theobaldia and Culex, and obtain their buoyancy by means of a pair of
air-chambers or floats situated one on each side. The larvae feed at, instead
of below, the surface of the water,* and occupy a horizontal position instead of
a more or less vertical one as in other genera of mosquitoes.
The genus Anopheles, which comprises the malaria-carrying mosquitoes, has
four representatives in this country.
It is because of this fact that Anopheles larvae can be destroyed by a fine arsenical dust-spray
which settles on the surface of the water and which they eat. Such dust-sprays, containing " Paris-
Green," are now very widely used in anti-malaria measures, but they have no efiect on the larvae of
non-malarial mosquitoes {Culex and Aëdes).