LOO BRITISH BLOOD-SUCKING FLIES B R A C H Y C E R A — T A B A N I D A E 101
The Museum specimens of this species vary in length from n to nearly
i6 mm. It is a well-marked species, easily separated from T. julvus by the
lack of conspicuous yellow pile, and from T. rusticus by the presence on the
outer (extensor) surface of the hind tibiae of a more or'less conspicuous and
regular fringe of black hairs. The eyes are densely hairy in the male, only
moderately so in the female, \-errall ^1909, p. 390^ describes the eves of the
female as " opalescent green with peculiar shifting spots according to the
point of view, and these spots are rather few in number and are not arranged
m rows, but there is also a slight crossband."
In the British Isles up to the present time T. nignfacies seems to have
been met with only in Essex, Kent and Dorset ; writing of Colonel Yerbury's
captures of this species at
^^'alton-on-Naze in 1907,
A'errall (1909, p. 391)
states that the insect
" occurred on the salt
marshes near the town
from August 8th to 22nd,
and upon one occasion
Colonel Yerbury saw them
in some numbers amongst
sheep ; the males were
obtained by sweeping the
herbage." The species
apparently occurs only in
August in this country.
i'lG. 35.—r. mgrifacies Gobert. Head.
In Brittany, Surcouf (1924, p. 52) found larvae of this species in seaweed on
the sea-shore, and also took a male in the act of emerging from its pupa-case,
which was sticking out of the sand. It is possible that T. mgrifacies and certain
other species of the same subgenus {Ochrops) prefer to breed in mud or sand
which IS periodically flooded by the tide. In Xorth Africa, on the shore of
Jerba Island, Tunis, Professor Seurat of the University of Algiers, found larvae
of T. {Ochrops) senrati Surcouf m large numbers in damp sand beneath masses
oi Posidonia (a marine flowering plant) cast up by the sea (see Surcouf, 1924,
p. 52). Surcouf also mentions the finding of adult females of the same species
on seaweed on the coast of Algeria. The above-mentioned larvae were feeding
on sand-hoppers {Talitrus lonista Pall.), and other larvae of T. senrati were
found by Professor Seurat on November 14th, 1923, living under the same
conditions on the shore of the bay of Algiers.
Tabanus sudeticus Zeller
(Fig. 36 and Plate 30)
Those who have had practical experience of this and of the two following
species {bovimis Linn, and verralli Oldr.) in life will readily confirm Colonel
Yerbury's observation that they " make a deep hum when flying round one
quite unlike the note produced by the smaller Tabanidae." The sound
emitted by these magnificent flies is, in fact, in proportion to their size, since
these three are the [bulkiest of all British Diptera. As a rule, sudeticus is the
largest ; a large female of T. verralli may measure just over 23 mm. inch)
in length, while the length of the largest sudeticus in the Museum is exactly
I inch. Flies such as these are exceeded in size by very few representatives of
their genus in any part of the world.
The eyes in all three species are bare, and in life devoid of bands, and
according to Brauer (1880, pp. 184, 185), while the eyes of the male of bovinus
are entirely green, those of the male sudeticus are " blackish with a coppery
sheen, the larger facets greyish, the smaller ones more reddish." The males
of sudeticus and verralli have the facets in the upper part of the eye much
larger than the lower facets and sharply divided from them, but in bovinus the
eye-facets in both sexes are uniform. The eye-colour of the female is given by
FIG. 36.—r. Zeller. Head.
Brauer as emerald green in bovinus and " always blackish-brown with a
coppery sheen " in sudeticus.
The female sudeticus is readily separated from the other two species by the
very dark colour of the abdomen, even at the base and on the underside.
In the British Isles the typical form of this species, despite its name, appears
to have a northern distribution, the Museum specimens being all from Scottish
localities, except one male from Ambleside, Westmorland^ A form of this
species, named sudeticus uieridioualis by Goffe (1931, p. 74) occurs in Surrey
and other southern counties along with verralli. In Britain this species
is usually on the wing only in July and August, though Continental
authors include June in its season. T. sudeticus is generally distributed on the
Continent.
In a field-note attached to one of the specimens taken by him at Crosswood,