76 BRITISH BLOOD-SUCKING FLIES
Glossina, but transmission is said to be entirely mechanical, through contamination
of the proboscis of the fly during feeding. short account of this disease,
particularly in Egypt, is given by Efiflatoun (1930, p. 19). Other diseases which
horse-flies are known or suspected to carry, in other parts of the world, include
anthrax, "swamp fever", and anaplasmosis of cattle (see Philip, 1931,
pp. 10-12 ; Cameron, 1926, 1935 ; and Schwardt, 1936).
PREVENTIVE AND PROTECTIVE MEASURES
In this country Horse-flies are rarely so numerous as to make control
measures worth while, but in a badly infested area some reduction may be
achieved by drainage of ponds and swampy areas which provide oviposition
sites for the flies (see under Chrysops, below, p. 78), or by oiling the surface
of standing water (see above, p. 72). Grazing animals derive relief from the
provision of a shed, or other shelter, preferably with a curtain of canvas over
the doorway ; the flies, being lovers of sunlight, rarely penetrate into the
darkened interior, and the canvas curtain helps to dislodge those flies clinging
to the animal as it enters.
Repellants are very limited in their effectiveness, being difficult to apply
sufficiently thoroughly, and soon dissipated from an animal working in the open
air. Moreover, unless made up and applied with extreme care, they entail
considerable risk of damage to the animal's skin. Various formulae have been
tried in the United States, and the whole subject of stock-protection is admirably
summarised by Philip (1931, pp. 70-73)-
No preparation seems yet to have been devised which is powerful enough
to repel Horse-flies and yet suitable for application to the human skin.
THE GENERA OF BRITISH TABANIDAE
In recent years the names of several of the genera of British Tabanidae
have been changed, or changes of name have been proposed. Owing to splitting
up of the old genera Therioplectes Zeller and Atylotus Osten-Sacken, the British
species formerly included in them have been transferred to Sziladynus Enderlein
and Ochrops Szilady respectively ; in this volume the two latter are regarded
as subgenera only, and are included under Tabanus Linnaeus. There has been
much dispute about the proposed revival of the names published by Meigen in
1800, and the matter has been referred to the International Commission on
Zoological Nomenclature. If these names were revived the name Haematopota
would have to be replaced by Chrysozona—a change which has already
been adopted by Goffe in his monograph of 1931, and by many Continental
workers—but pending a decision on this point the better-known name
Haematopota is used in this work.
The keys in the section of this work dealing with Tabanidae are intended
to apply to female specimens of British species only.
A. Wings with a conspicuous cross-band of dark brown or black Chrysops Meigen
B. Wings mottled grey and white Haematopota Meigen
C. Wings clear ; sometimes with a brownish tinge towards the foreborder, but never with any
definite markings Tabanus Linnaeus
BRACHYCERA—TABANIDAE 77
Subfamily PANGONIINAE
Genus CHRYSOPS Meigen
Of the sixty valid species of this genus which down to the year 1926 had
been recognised as occurring in the Palaearctic Region only four have so far
been met with in the British Isles. Verrall's suggestion (1909, p. 439) that
Chrysops rufipes Meig. and C. par alíelo gramma Zeller are likely to occur in
Britain has not yet been justified. Although more than one species of Chrysops
is often locally abundant and troublesome in the south of England the genus
does not seem to be very plentiful in Scotland. The genus Chrysops is the only
representative in this country of the sub-family Pangoniinae, characterised by
having spurs at the tip of the hind tibiae.
In Chrysops caecutiens, C. quadrata and to a lesser degree in C. relicta
there is a striking difference between the sexes in the colouration and pattern
of the abdomen (cf. pi. 16). The dark transverse band on the wings, though
present in both sexes, is usually m-ore sharply defined in the female than in the
male. In the resting position the wings are flat and half open, i.e. somewhat
wider apart at the tips than in Tabanus.
In life the eyes of all species of Chrysops are extremely beautiful, even when
compared with those of other Tabanidae which as a family are noted for the
beauty of their eyes. The ground colour is golden- or reddish-green, and is
marked with purple spots and lines.
The females of the various species of Chrysops, which attack human beings
as well as domestic animals, are often extremely bloodthirsty and are capable of
inflicting a severe bite. Males of this genus are frequently to be met with upon
flowers, especially Umbelliferae and, according to Jones (1922, p. 41), Senecio
and Mentha arvensis.
The various species of Chrysops deposit their eggs upright, usually in a
single layer forming variously shaped batches upon the leaves and stems of
reeds or other plants overhanging flowing or stagnant water. The following
account by Professor J. S. Hine of oviposition of Chrysops moerens Walker as
observed by him at Sandusky, Ohio, is worth quoting.
" The female," writes Professor Hine, " alights on a leaf with her head
downward and begins the process by pushing the tip of her abdomen forward
toward the under part of the thorax and placing the protruding end of an
egg against the leaf. The end sticks fast by means of a glue-like substance
which accompanies it, and she moves the tip of her abdomen back to its
normal position, thus freeing the egg. By similar movements one or two
eggs are placed by the side of the first, and two or three more to the other
side of it. The unfinished end soon becomes V-shaped ; she moves slowly
forward, lifts the tip of her abdomen to one arm of the V and places eggs
along it until the apex is reached ; then changes to the other arm of the V
and places eggs along it down to the apex again. It was noted in specimens
of this species that sometimes a female would place as many as three rows
of eggs on one side before changing to he opposite side. It is only necessary
to study a mass of these eggs in order to see the precision in reference