JS BRITISH BLOOD-SUCKING FLIES
to one another, with which the different eggs are laid." (See Hine, 1906,
p. 37^
In places where these flies are abundant the elongate eggs, which are white
when newly laid, and subsequently become opalescent brownish (dark brown,
or e^•en shining black in some exotic species), are deposited in countless myriads,
closely packed in sheets. The larvae live in water, mud, or the matted and
sodden remains of aquatic vegetation, and both larvae and pupae are of the usual
Tabanid type.
The larva may be distinguished from those of Tabanus by the last segment
of the antenna being considerably longer than the preceding one, instead of
being the same length or much shorter. Pupation apparently takes place as
a rule in the mud, in moist earth or in damp sand, close to the water's edge.
According to Stammer (1924, p. 126), the larvae of Chrysops are not predaceous
and show no tendency towards cannibalism when kept together in captivity.
The same writer states (1924, p. 127^ that the development cycle in Chrysops
lasts only one year.
Although British species are not concerned, it may be of interest to remark
that the only members of the family Tabanidae hitherto proved to play a part
in the transmission of human disease belong to the genus Chrysops (see above,
p. 7.0.
Schwardt (1936, p. 59) states that where Chrysops is breeding in the mud
round the margins of a pond in such numbers as to be troublesome, some
measure of control can be achieved by clearing the shores of the pond so that
within 10 or 12 feet of the water's edge there are no stones or sticks to provide
oviposition sites, and no plants or débris projecting above the surface of the
water. Sudden changes in level of the water, as, for example, when heavy
rains follow a prolonged drought, also help by drowning the pupae, or driving
them out of the mud to be destroyed by predators.
KEY TO THE FEMALES OF THE BRITISH SPECIES OF Chrysops
1. Ground-colour of body entirely shining bronze-black. Hind margins of segments with
taT^-ny pubescence (Plate 19) sepulcralis Fabr.
Ground colour of base of abdomen predominantly yellow 2
2. Upper surface of second visible segment with a black mark like an inverted V in centre,
usually sharply defined, but sometimes indistinct. Middle tibiae black, paler at base
(Plate 16) caecutietis Linn.
Second abdominal segment otherwise marked. Middle tibiae yellowish brown, blackish
at apex 3
3. Second abdominal segment orange yellow with a single black spot which varies from almost
nothing to a large rectangular or quadrate blotch (Plate 17) quadrata Meigen
Second abdominal segment yellow, bearing two black lobes inchned downwards and outwards,
usually united at their bases (Plate 18) relicta Meigen
Chrysops caecutiens Linnaeus
(Plate 16)
The figures in the plate afford a fairly accurate picture of the striking
sexual differences shown by C. caecutiens in the colouration and markings of the
thorax, abdomen and wings. Although similar contrasts are seen also in
BRACHYCERA—TABANIDAE 79
Ch/ysops relicta (p. 81) and to a lesser extent in C. quadrata (p. 80), they are
so pronounced in caecutieiis as to suggest that the sexes belong to different
species. It should be noted, however, that on the ventral surface of the basal
half of the abdomen of the male C. caecutietis there is a light patch on each side,
which frequently extends on to the dorsal surface and then forms a more or
less conspicuous fleck on each side of the second segment.
Verrall (1909, pp. 425, 427, figs. 241, 243) gives black and white illustrations
of the eye-markings of both sexes of caecutiens. In the males the eyes touch
for less than one-third of the distance between the occiput and the antennae;
the facets on the upper part are dilated and purplish brown in death, on the
lower part small and blackish. In the females the eye-facets are all equal.
The length of British specimens of C. caecutiens as represented by the
specimens in the British Museum varies from 8 to 10-5 mm. in both sexes.
C. caecutie7is is widely distributed in the south of England and in the
midlands, and has been taken all over Great Britain up to the north of Scotland.
Verrall (1909, p. 428) considered that it was rather less common than relicta,
but later records show caecutiens to be the commonest species of the genus, at
least in the south. It was taken as early as May 24th, in S. Devon by Col.
Yerbury, and is on the wing till the middle of September. Jones (1920, p. 7)
found this species extremely abundant in the New Forest, and writes : " For
several days in July I was forced to give up collecting owing to the sight of
both eyes almost disappearing, chiefly the work of Chrysops caecutiens, who
delighted to bite on the forehead, just above the eye." Mr. F. C. Morgan,
curator of the Hereford Museum, in a recent inquiry about this species, states
that it is locally known as the " thunder fly," and that it is troublesome in
biting dogs.
Surcoût (1924, p. 47) has described the oviposition of this species on the
leaf of a reed as witnessed by him in July, 1914, at Saint-Gobert (Aisne), in
F ranee. The eggs hatched on the following day, and the young larvae, which
were barely i mm. in length, at once slid down into the water at the foot of the
reed.
The larval and pupal stages of C. caecutiens are passed in mud on the margins
of streams. In mud piled up beside a rapid stream in a meadow, Beling (1888,
p. 2) found, on July 8th, 1887, a larva, five pupae and several pupa cases ; the
pupae were collected and produced two males and three females between
July nth and 15th. Elsewhere in north Germany larvae of caecutiens were
found in abundance by Stammer (1924, p. 123) in the mud bordering a
small, sluggish stream, the margins of which were fringed with tall beech and
ash.
According to the same author (pp. 126, 127) the larva of this species feeds
on decaying organic matter, and in all probability is not predaceous. He kept
five larvae together for four weeks in a small vessel without supplying them
with animal food. They did not attack one another, and the contents of their
intestines appeared to consist only of the fine mud in which they were living.
It is indeed asserted by Stammer that no one has observed a predaceous mode
of life in a Chrysops larva. The larva may attain a length of 17 mm., and is