122 



KNOWLEDGE, 



[July 1, 1891. 



is, at the outside, not more than that between closely 

 allied species. It is true that the virulence of the " bite " 

 of these creatures in tropical countries is much greater 

 than it is here ; ;nid, when one remembers the frightful 

 effects that are sometimes produced on the human body 

 by these little pests, and the strenuous efforts that are 

 made, and the elaborate precautions that are taken, 

 whether in the way of oily unguents, of curtains and nets, 

 or even of burying the body in the sand, to guard against 

 their attacks, it is no doubt disappointing to discover that 

 after aU there is nothing so very remarkable in the 

 creatures, and that they can hardly be distinguished from 

 insects ^nth which we are familiar at home. Nevertheless, 

 it is a fact, which we must constantly bear in mind, that 

 the insects to which these names are applied are to all 

 intents and purposes identical both in structure and in 

 life-history, and we are therefore justified in making no 

 distinction here. Moreover, there is no doubt that, even 

 in the matter of virulence, our own gnats vary a good deal, 

 both according to season and to the temperament and sen- 

 sitiveness of the person attacked. "We must not, however, 

 fail to note that there are other flies, belonging to difierent 

 families, that are also blood-suckers, and in some cases 

 are ahnost as troublesome as the true gnats and mosquitos. 

 This is specially the case with the small flies called Simvlia, 

 which are closely allied to the family Culiridn-, and are, it 

 w^ould appear, sometimes called mosquitos in America. 

 Such insects, however, are not referred to here, and what 

 we have to say about " gnats and mosquitos '' concerns 

 only the family CuliriiUe, and, in fact, the genus Cith-.r. 



Of the term " midges " it is somewhat more difficult to 

 fix the application ; it is indiscriminately used of at least 

 two types of flies, quite distinct from one another, one, in 

 most respects except persecuting powers, similar to the 

 gnats and mosquitos, the other very different in appear- 

 ance, and at first sight more like tiny moths than flies ; 

 but it appears also to be popularly used in a loose manner 

 for small and annoying insects of whatever kind, without 

 any definite conception as to the actual form intended. It 

 is obvious, therefore, that when the entomologist hears 

 people talking vaguely of gnats and midges, it is not 

 always easy to understand exactly what insects are being 

 referred to. 



With these preliminary precautious, and bearing in mind 

 that not every small, long-legged, fragile fly is a gnat in 

 the sense in which the word is here used — i.e., a blood- 

 sucking gnat — we may now proceed to consider first what 

 sort of being a blood-sucking (jnat or iiios(]>titii really is, 

 referring afterwards to those which seem to be more cor- 

 rectly called iiiidi/is. The photogi-aphs on the accom- 

 panying page will give a pretty good idea of the general 

 form of a gnat. A small head, a considerable portion of 

 which is occupied by the compound eyes, is attached by 

 means of a short neck to a huge globular thorax, so dis- 

 proportionately large as to give the insect, when viewed 

 sideways, a hump-backed appearance. Behind this the 

 trunk is completed by a long, slender, cylindrical abdomen. 

 A long, straight, beak-like appendage, carrying the mouth 

 oigans, points forward from the head, and a pair of more 

 or less tufted, thread-like antennae fonn an excellent head- 

 gear, counterbalancing this above. From the upper part 

 of the thorax spreads at each side a single membranous 

 wing, exquisitely delicate, and gi-acefuUy fringed along its 

 hinder edge ; the place of the customary second pair is 

 taken by the " poisers," long knobbed stalks, as ah-eady 

 described in the other di\-ision of flies, but proportionately 

 much larger than in those. From the under surface 

 of the thorax start the three pairs of inordinately long 

 legs, upon which, when at rest, the body is, as it" were, 



slung up off the ground, as if on springs. Though the legs 

 consist only of the ordinary parts, yet the divisions seem at 

 first sight to be more numerous than usual, by reason of 

 the great proportionate length of some of the parts, and 

 particularly of the tarsi, or feet, which in the hind pair 

 constitute more than half the entire length of the leg, the 

 leg itself becoming nearly three times as long as the abdo- 

 men. The insect is beautified by the addition, on various 



parts of the body, of 

 minute iridescent 

 scales (Fig. 1), similar 

 to those of butterflies 

 and moths ; rows of 

 them adorn the wings, 

 especially along the 

 Fig- 1- nervures. 



A marked difference appears between the sexes. The 

 male can be distinguished by the extraordinary development 

 of the antenn;e, which, as frequently in insects of that sex, 

 are. if one may judge from their structure, far more deUcate 

 organs of sense than those of his mate. The antennre of 

 the female consist of a string of cylindrical joints like long 

 beads, each provided with a circlet of fine hairs of no very 

 great length. Those of the male, however, while similarly 

 constructed, have the brushes much longer and more 

 thickly set, especially at the base, for the extreme tip is 

 almost bare. In the photograph the hairs of the female 

 are indistinct through their extreme tenuity, and the 

 charming symmetry of form and arrangement which those 

 of the male naturally exhibit is unfortunately destroyed 

 because the insects have been preserved in balsam, and it 

 is impossible then to ensure that appendages so dehcate 

 should be spread out with all the hairs in proper position ; 

 no conception, therefore, of their great beauty can be 

 formed fi'om a specimen so preserved. 



The greatest interest, of course, attaches to the pro- 

 boscis, for herein are contained the weapons of attack. 

 In this, again, the sexes difi'er greatly, and it is against 

 the female only that the charge of blood-sucking can be 

 substantiated. The male is an inoffensive creature, and 

 usually remains in his native haunts, not invading our 

 apartments ; for it must be remembered that these flies, 

 like those treated of before, pass their early stages out of 

 doors and enter our houses only when fully grown. The 

 straight, cylindrical spike projecting from the head, though 

 itself no thicker than a hair, is a tube, or rather trough, 

 terminated by two small fleshy lips, the dwarfed represen- 

 tatives of the two large folding leaves which terminate 

 the proboscis of the blow-fly. This tube represents the 

 labium of the normal insect's mouth, and concealed 

 within it lie the much finer picrciiii/ organs ; for the so- 

 called " bite,'' like that of the bed-bug, consists really of 

 a boring and sucking operation. Along by the upper slit 

 of the trough lies a long bristle-shaped organ, which 

 represents the labrum, or upper lip, and of course all the 

 rest of the mouth organs, except the palpi, he between this 

 and the labium, i.r., in the trough of the latter. The 

 mandibles and maxilla?, which in insects that feed on 

 solid food are efficient biting weapons, are here, as in the 

 bed-bug, replaced by fom- fine-pointed, needle-like bristles, 

 the maxillie being further barbed at the tip like a savage's 

 spear, and the mandibles slightly broadened into a lancet- 

 shaped tip. Besides these, another piercing bristle is 

 found, which is an appendage of the labium itself. Thus 

 there are no less than six boring organs, all contained 

 within a sheath which is itself almost of hairlike fineness. 

 The sheath itself, like so many other parts of the body, is 

 beautifully ornamented outside with abundance of battle- 

 dore-shaped scales. At its base are two short jointed 



