78 



KNOWLEDGE. 



[April 2, 1894. 



It is a cruel-looking, grey-bodied insect, with speckled 

 wings, and somewhat smaller and slenderer than a blue- 

 bottle fly. During life its eyes are strongly suggestive of 

 an evil nature, for they are green, with three or four 

 crimson bands across them. Their brilliancy, however, 

 disappears after death. 



This fly, which is sometimes called the cleg, belongs to 

 a family of e\'il repute, the Tabanidce, which, from their 

 persecutions of farm quadrupeds, have acquired, as a group, 

 the name of horse-flies. Kirby mentions a striking instance 

 of the severity of the attacks of these creatures. He was 

 driving with another entomologist through Cambridgeshire, 

 when the horse became " bathed in blood flowing from 

 minute wounds made by the knives rnd lancets of various 

 horse-flies." The larger members of the family are also 

 known as gadflies, a name that has the misfortune of 

 being applied to other flies as well, which are troublesome 

 to cattle as internal parasites, and whose life-history, 

 therefore, is totally difl'erent from that of the Tahayiida. 

 Much confusion has thus originated, and can only be 

 avoided by using the scientific instead of the popular name. 

 It must, therefore, be clearly understood that throughout 

 this paper, when using the term gadfly, we are speaking 

 of the non-parasitic gadflies of the genus Tahanus, and not 

 of the parasitic ones of the genus (Estrus, which belong to 

 quite a different family, and have no stinging power at all. 

 The Tabani have further acquired the name of breeze-flies, 

 in consequence, it is said, of the loud buzzing they make 

 during their rapid and headlong flight. These larger kinds 

 are not nearly so common in this country as the cleg, and 

 it is fortunate, at least for our cattle, that such is the case, 

 for with their larger size is associated a proportionately 

 severer bite. There is, however, this to be said in their 

 favour, that, in consequence of their buzzing, you know 

 when they are coming, and can be on the look-out. Such 

 is not the case with the wretched little cleg, which has a 

 silent and almost stealthy flight, giving no warning of its 

 appi'oach, but settling on the skin in a calm and determined 

 way, though with so gentle a touch that the victim is quite 

 unconscious of its presence, if its arrival does not happen 

 to have been seen. It does not run over the skin seeking 

 a good place for attack, but sets to work at once at the 

 spot on which it has alighted. By the time the prick is 

 felt, the six lancets with which the mouth is furnished 

 have already been plunged deep into the skm, and are 

 fixed therein so firmly that, unless the fly chooses to with- 

 draw them, some little force is needed to dislodge the 

 creature. The after efl'eet of the puncture seems, as is 

 generally the case with punctures of this sort, to vary with 

 the sensitiveness of the person attacked. To some it 

 causes only temporary irritation, in others it produces 

 swelling and inflammation which do not subside for some 

 days. 



In the articles on gnats and mosquitos above alluded to, 

 we pointed out that the persecuting power is characteristic 

 of one sex only ; the males are harmless and inoffensive, 

 and it is in the feminine mouth that all the virulence 

 resides. The same is true of the Tabanidai : the males 

 have much smaller mouth organs than their partners, and 

 have two lancets less, the knife-like mandibles being absent, 

 and they regale themselves with sweets from flowers instead 

 of blood. It is not a little remarkable that in the case of 

 all the insects we have already dealt with, whether the 

 power of irritation resides in the head or the tail, it is 

 without exception the females, whether prolific or abortive, 

 that possess the persecuting power. To this rule, however, 

 the Hemiptera, which we shall consider presently, constitute 

 an exception ; in them both sexes possess and use the 

 piercing bristles. 



Fia. fi. — CTolden-eye {Chrysops 

 crBcuHeiis). Magnified two dia- 

 meters. 



Another very brilliant but exceedingly vicious member of 

 the Tabanidm is the " golden eye " {Chnjsups ccecutiens) 

 (Fig. 6). It is a trifle larger than the cleg ; its black body 

 has an orange band at the 

 base, interrupted with _ V 



black markings ; its wings 

 have a dark cloud along 

 the margin, a dark band 

 stretching across the 

 middle, and another 

 smaller one towards the tip. 

 Even in these parts it is a 

 handsome insect, but it is 

 in the eyes that its greatest 

 glory lies. On seeing the creature for the first time one 

 can hardly suppress an exclamation of admiration and 

 delight, as one gazes at the blaze of brilliance with which 

 the eyes sparkle — -it is as though the brightest of gems 

 were set in glowing masses over the head ; the ground 

 colour is brilliant golden-green, and scattered over this on 

 each eye there are five deep crimson or purple spots. The 

 hind border of the eye also is set with the same intense 

 colour, and then, as with a gem, there is a change of the 

 appearance as it is regarded first from one point of view 

 and then from another. Like the cleg, this fiery creature 

 is silent in its flight, and the first hint of its proximity is 

 its own brilliant self seen calmly resting, perhaps, on one's 

 coat-sleeve. If this be so we can afford to admire it at 

 leisure, but if it should have dropped silently down on to 

 the bare flesh, the first involuntary thought of admiration 

 will soon be banished by a sharp twinge of pain, and we shall 

 hasten to shake or brush oft" the offender, heedless of its 

 gems and their lustre. The mouth organs in all the female 

 Tabanidx form a vicious-looking beak pointing downwards 

 from beneath the head, and as the antennae also have a 

 rather cruel aspect, being short and stiff and curled upwards 

 like little horns, the face of the insect forms a pretty good 

 index to its character. 



The gadfly of the ox (Tabanus bovinus) is a very fine 

 insect, the bulkiest of all our British Diptera. Like its 

 brethren it has a broad, flattish body, each segment of 

 which is dark at the base and pale at the apex ; in the 

 centre the pale margins expand into pale triangles, which 

 form a line down the middle, and by their artistic effect 

 take off something of the otherwise awkward breadth of 

 body. The larva of this fine insect is a footless grub 

 which lives underground, where it appears to feed on the 

 roots of plants and vegetable refuse. While still under- 

 ground it changes into a spiny chrysalis, and when about 

 to become a perfect fly this chrysalis works its way up 

 through the soil by means of its spines and bristles. In 

 this resting stage it is of course blind, like pupnsin general, 

 and how it knows in what direction to move so as to reach 

 the surface must be left to conjecture. The larva is full 

 grown in May, and the perfect fly appears during the 

 summer, when it becomes a great plague to cattle in 

 districts where it is common, by piercing their hides by 

 means of its powerful set of six lancets, and sucking their 

 blood. This is certainly a strange revolution in tastes ; 

 that an insect which in early life is a nibbler of roots 

 should become in adult age a sucker of blood is hardly 

 what would have been expected, though it is by no means 

 an alteration without parallel amongst the order Diptera. 

 A change from solid to liquid food is necessitated by the 

 altered form of the mouth organs, but still there are plenty 

 of vegetable juices available, and it would have seemed 

 more natural had some of these been selected. There are 

 several other species of Tahanus, which closely resemble 

 the gadfly in form and adornment, and which are some- 



