84 BRITISH BLOOD-SUCKING FLIES
between eleven and twelve o'clock, in groups of from six to nine individuals
above pine stumps (as seen by Colonel Yerbury at Nairn on July 9th, 1904) ;
they alternately rise and fall between 5 and 12 feet from the ground, and
when the sun is obscured, rest on the pines ; I have never seen this habit, but
have commonly found them resting on posts or rails, or towards evening on
flowers."
Major Austen (manuscript notes) wrote : " It may be of interest to remark
that Africa is peculiarly rich in species belonging to Haematopota and evidently
represents the head-quarters of the genus. Thus at the present time (1925)
the number of known Palaearctic species amounts to some twenty-seven, while
the Oriental species similarly number forty-nine. From the Ethiopian
Region, however, the Museum possesses representatives of no fewer than one
hundred and twenty species, a few of which have yet to be described, and it is
safe to say that the figure mentioned will be considerably exceeded when all
the African species of Haematopota are known."
KEY TO THE FEMALES OF THE BRITISH SPECIES OF Haematopota.
1. Antennae conspicuously longer than the head, more than one and a half times length of
head from back to front ; first antennal segment cylindrical, not swollen, approximately
equal in length to third segment ; wing markings rather pale italica Meigen
Antennae not conspicuously longer than head, not more than one and a half times length of
head from back to front ; first antennal segment not cylindrical, but more or less ovoid,
shorter than third segment
2. Third antennal segment black throughout, rarely ven^ slightly reddish at base ; first antennal
segment short, very distinctly swollen, and shining black (Plate 21) crassicornis Wahlb.
Third antennal segment more or less reddish on basal half ; first antennal segment not so
conspicuously swollen, usually constricted near tip, and only apical part shining 3
3. Middle and hind femora more or less yellow or reddish ; upper surface of abdomen with a
pair of sharply defined pale spots on each segment except possibly the last. . .bigoti Gobert
Femora entirely blackish ; paired abdominal spots poorly defined, and absent from first, or
first and second segments (Plate 20) ptuviatis Linn.
Haematopota pluvialis Linnaeus
The common Dun-fly or Cleg. (Plate 20)
Of British blood-sucking flies other than midges, mosquitoes and blackflies,
this species is one of the commonest, most aggressive and most generally
distributed, occurring throughout the British Isles. Verrail recorded it from
May 28th to September i6th (1909, p. 336), and Goffe (1931, p. 63) adds :
" occasionally even to October." The specimens in the British Museum vary
in length from 8 to 11 mm. in the male and 7 to 11 mm. in the female. Krober
(1925, p. 51) gives the distribution of this species as Europe, Siberia and North
Africa.
So long ago as 1834 Curtis wrote of this species : " . . . the females,
which attack both men and horses, sometimes appear in myriads without one
male." Although the males of H. pluvialis, as of most Tabanidae, are not
easily met with (compare, however, H. crassicornis, below), there are occasionally
striking exceptions to this rule. Thus Krober (1922, p. 157) writing
of H. •bluvialis, states : " On one occasion at Curslak near Hamburg, in the
BRACHYCERA—TABANIDAE 85
early morning of June 12th, on some railings closing a cow-pasture," he " met
with a good 200 males, all freshly emerged, and not a single female among them."
Jones (1922, p. 40) took males of this species, among others, over muddy pools
in the bed of a partially dried-up stream in the New Forest, and records that,
like Chrysops they are great " mud-sitters."
Cragg (1912) has described the method of feeding of pluvialis.
" After a short preliminary investigation in which the labium appears
to be used as a tactile organ, the piercing styles are inserted by a series of
short sharp forward thrusts of the thorax, the labium being retracted and
the labella everted behind the rest of the proboscis, and the maxillary palps
extended in front. As the wound is deepened the fly elevates itself on its
hind legs, till the abdomen is tilted up at an angle of 45° or so, the forelegs
being meanwhile extended in front of the proboscis, with their tibiae held
parallel to the surface. While in this position the abdomen gradually
distends and slight peristaltic movements can be seen in it. [These are
attributed by Cameron (1934, p. 214) not to peristalsis, but to rhythmic respiratory
movements.] In a short time a clear fluid begins to exude at
the anus, and this goes on as long as the insect feeds, the fluid becoming
tinged with blood towards the end of the meal, and even in some cases
appearing to consist of unfiltered blood. Several times during the process
the mouth parts are withdrawn a little and again thrust in ; finally they are
withdrawn by a few sharp jerks and the fly, after resting a moment to clean
its proboscis with its forelegs, flies away. A small drop of blood usually
oozes from the puncture, and a faint ring of hyperaemia, with usually some
slight irritation, mark the site for a day or two. The pain caused by the bite
is usually trifling, less than that of a mosquito bite. Some individuals,
however, appear to be remarkably sensitive, and may suffer for days, even
a week or longer, from local irritation or inflammation \cf. Verrail (1909,
p. 329]. The fly takes about three minutes to obtain a full meal, and while
feeding it is not readily disturbed ; and the process can be watched on one's
hand through a pocket lens."
Cameron (1934, p. 214) found that unfertilised females in captivity would
not feed, a conclusion which was supported by the behaviour of specimens
caught in the field. A second meal was not usually taken until after oviposition,
which might be delayed from six to twelve days. This author also notes that
although engorgement usually takes three to six minutes {cf. Cragg's observations,
above), feeding might continue for as long as thirty minutes. He suggests
the tapping of a lymphatic instead of a blood-vessel as one cause of
protracted feeding.
For a very full account of the biology of Haematopota pluvialis Meigen,
see Cameron, 1934.
Haematopota crassicornis Wahlberg.
(Plate 21)
In both sexes H. crassicornis is a much blacker-looking species than H.
pluvialis, and the characters specified in the key on page 84 for the separation