i
68 BRITISH BLOOD-SUCKING FLIES
those who are not entomologists when they learn that k is really a British
insect The Horse-flies, which are world-wide in their distribution, are also
a Large family, the total number of species described up /^SB
mclurive amounting to some 3,000. In 192S, according to Lmdner (19 5-
p I38\ over 400 species were known to exist in the Palaearctic Region, and
. 8 are found in the British Isles. They belong to the genera CIp'sops, Haema-
~topota and Tahanus ; the genus Pangomns^ remarkable for its elongate
proboscis, does not occur in this country, though a number of species are found
in southern Europe.
APPEARANCE
In appearance the Tabanidae are stoutly built flies with ^ large head,
which in the males is almost wholly composed of the eps In all the British
species the eyes of the males meet together in the middle line, but those of the
f L a l e s are distinctly, and often widely separated by the Jrons upon which
mav be seen one or more bare, shining/r...^./ calU, which are of great importance
in the determination of species. The males often have an - e a in the ^
portion of the eyes composed of larger facets than those below, the extent and
sharpness of demarcation of this area varying in different species. ^
In life the eves of Tabanidae usually exhibit golden-green or purple markings,
which are of v-alue for the identification of the species. They are especially
brilliant in the females of Chrysops and Haematopota, which, as pointed out
by Girschner (1887, p. 156), possess probably the finest eyes of all insects
t i i s author, in an interesting discussion of the practical significance of eye
colours in Diptera, suggests that they may be correlated with a poorly developed
sense of sight. After death the colour of the eyes rapidly change to a dull
br'wn? unfil scarcely a trace of the markings remains. In the plates to this
work the eyes are shown as in dried specimens, from which perforce the ongina
drawings L d to be prepared, but in many cases notes on the natural colour
and pattern are given in the account of the species concerned.
The eye-colours can be revived to some extent by placing the dried specimen
in a relaxmg tm on damp sand covered with blotting-paper, but the markings
of the b o d; are likely to receive permanent injury by this treatment.^ G ffe
(1932., p. 16) recommends immersion in a solution made up as follo^^s . AceUc
\ T d i ^ J \ . p a r t ; glyce..ne, ^ part ; soln. of perchlor^de of .nercu^^^
PhaZ. str ngth), i part; rectrfied sp^r^t, parts. This can be used to
festore the evf-markings in dried specimens, which, if then enclosed m a glassstonnered
glass tube, will retain their colours indefinitely.
T n f on! of the ey^s project conspicuously the antennae which are composecl
of three segments, while below the head in all the British species is normally
visible the L s h y proboscis or lower lip which encloses the piercing hP-JThe
palpi, which lie one on each side of the proboscis, are swollen and fleshy
L d differ in shape in the two sexes. The body is clothed with short hair, which
unfortunatelv is readily rubbed off in captured specimens, so that they are often
sadly altered in appearance, and bear little resemblance to the same species
BRACHYCERA—TABANIDAE 69
when freshly emerged.* The large bristles known as macrochaetae, which are
a conspicuous feature in certain other families such as the Asilidae (Robberflies)
are entirely wanting in all Horse-flies. In coloration as in the shape of
the body. Horse-flies throughout the world show relatively little variation, and
our British species are very similar in appearance to many of those belonging
to the same genera found in Africa, India and elsewhere.
OCCURRENCE AND PIABITS
Horse-flies may be met with throughout the summer in fields, open spaces
in woods, or by the roadside in the country, where, given a good season and
favourable weather conditions the bloodthirsty females are often a scourge to
man and beast. Thus Dr. C. Walton (1918) writing of blood-sucking flies as
observed by him in the Aberystwith area of Cardiganshire during the period
1913-16, mentions counting between thirty and forty Haeinatopota pluvialis
(pi. 20) on a man's back on June 28th, 1914, and states that on June 21st, 1915,
he " killed 200 upon four working horses in a few minutes." On a subsequent
page, referring to the summer of 1916, he speaks of working farm horses
being " driven frantic and difficult to control " by the attacks of Tabanus
sudeticus (pi. 30). Of the latter species. Dr. Walton remarks : " their
abundance may be judged when I say that I could easily fill a killing bottle in
half-an-hour from a pair of horses during the hay harvest (at Crosswood), and
a waggoner killed between twenty and thirty on one horse during a morning's
horse-hoeing." Most people at one time or another have noticed a herd of
cattle careering about a pasture-field with tails in the air, or, as farmers say,
" gadding." Such behaviour of the animals is doubtless due to sympathetic
action evoked by some form of fly-attack, but the actual species of fly concerned
in any given case, whether Warble-fly {Hypoderma), biting Muscid (see p. 115,
and pis. 37, 38) or Tabanid is usually very difficult to determine. For a discussion
of the species of fly concerned in producing " gadding, " see Appendix B.
The edges of woods are favourite haunts of certain species of Horse-flies,
and while resting in such a place on a hot. day, even when insects are not
numerous, one may frequently notice a Haematopota or two, or a specimen of
one of the smaller species of Tabanus crawling with much deliberation over
one's coat and making preliminary investigations with its proboscis. The
fe?7tales alo7ie suck blood : the males may be met with on flowers, or sometimes
hovering in the air like the Syrphidae (Hover-flies), but are best taken during
hot weather, when they descend to drink from pools and streams (see Jones,
1922, and Goffe, 1935).
Tabanidae sometimes take other food than blood. Writing of the North
American species Tabanus sulcifrons Macq., Hine (1906, p. 25), says : " I am
thoroughly convinced that the females take much other food than blood, and
do not believe it would be overstating the facts to say that specimens of this
* Tabanidae for determination should therefore be in the best possible condition, neither
crushed nor rubbed, and the colouration of the eyes, with the pattern of the markings, if any,
should always be noted before the specimen is killed.