Insects.] 



MUSEUM OF ANIMATED NATURE. 



355 



a double end is answered : thus the punctures made 

 for the primary object, viz. food, subserve a second, 

 and induce changes in the structure of the leaf 

 connected with the preservation of the young ; 

 we say the young rather than eggs, because the 

 aphides appear to be viviparous, and when what 

 are termed eggs are deposited, they are really 

 young aphides enclosed in a sort of cocoon, and 

 whicii pass the winter in a torpid state. Such at 

 least is ordinarily the case, and what is more re- 

 markable is this, that the aphides which make their 

 appeai'ance in full activity are females exclusively, 

 and prolific, being endowed with almost incredible 

 fecundity : but no males are found till the autumn. 

 It is not in fact necessary for the young female 

 aphides produced during summer to pair with a 

 male, which indeed would be impossible, as there are 

 no males to be found, yet these females go on pro- 

 ducing their young daily, these young themselves 

 still fertile ; and from a series of experiments sug- 

 gested by Reaumur, and conducted by some of the 

 French academicians, it was made manifest that nine 

 generations came successively into being, without 

 pairing, in the course of three months. Reaumur 

 calculated that one aphis may be the progenitor 

 during its life of 5,904,900,000 descendants. 



To return to the cells or galls made by these in- 

 sects : among the more remarkable are those pro- 

 duced, on the leaves of the black poplar, by a species 

 termed Eriosoma populi, which in June or July 

 may be seen carried about as it were by the wind, 

 and appearing like a little tuft of snow-white down. 

 Its body is in fact covered by long downy filaments, 

 which rather impede the use of its wings, though 

 they may contribute to its buoyancy, as it floats in 

 the air ; as among other aphides some are winged, 

 others not, nor are all covered with this white down, 

 which is perhaps peculiar only to the females, and 

 during a certain portion of the summer. How 

 this may be is not well ascertained. This species 

 punctures the leaves and leaf-stems of the poplar, 

 feeding on the exuded juice ; and each female, hav- 

 ing fixed upon a convenient spot, there remains 

 stationary, repeating her punctuies, till by degrees a 

 thick fleshy wall begins to rise around her on the 

 injured leaf, and at last encloses her in a cell, a 

 small opening remaining in some part. Here she 

 brings forth a numerous brood, and these in turn 

 enlarge the cell, and feed on the flowing sap, till, 

 having attained the winged state, they make their 

 exit, spread abroad, and found new colonies. 



Fig. 3504 shows the galls produced on the black 

 poplar by the Eriosoma populi, and the various forms 

 of the insects, winged, wingless, and covered with 

 down, both of the natural size and magnified. 



It is extremely common to see the leaves ot various 

 plants and trees curled up and distorted, with a host 

 of aphides embowered within the chamber thus 

 formed : the leaves of the raspberry bush are very 

 frequently thus affected, and become the nests of 

 these insects, into which, however, the lady-bird 

 (Coccinella) finds her way, and thins the living mul- 

 titude. It is also very common to see on the leaves 

 of the currant tree, numerous red bulgings irregu- 

 larly clustered together, which when examined will 

 be found to be concave underneath, and filled with 

 aphides (aphis ribis), feeding on the juices of the 

 leaf, which becomes thus diseased and deformed by 

 their punctures. See Fig. 3505, a leaf of the cur- 

 rant bush, distorted by these insects. 



In like manner the succulent twigs and tender 

 shoots of jjlants become warped and unnaturally 

 twisted, and even spirally contorted, by the opera- 

 tions of these insects, as seen at Fig. 3506. 



A pretty pseudo-gall is produced on the Scotch 

 fir (Hinus sylvestris) by one of the largest of our 

 aphides, the Aphis pini ; it is a scaled excrescence, 

 not unlike the fruit of the tree in miniature, and of a 

 reddish colour. It generally appears on the termi- 

 nal shoots, and may be found during the summer 

 months. (Fig. 3507.) 



While speaking of galls and other unnatural ap- 

 pearances resultuig from insects, we may observe, 

 that singular excrescences are often to be observed 

 on shrubs and trees, in which no larva; can be disco- 

 vered. These morbid tumours may have arisen from 

 disease originatins* in the branch itself, or produced 

 by some external injury, sometimes, perhaps, by the 

 attacks of insects. Fig. 3508 shows a branch of the 

 bramble thus diseased ; and Figs. 3509 and 3510, two 

 twigs of the hawthorn in a similar condition. 



From the morbid tumours, called galls, on the 

 tree^', resulting from a wound followed by the intro- 

 duction of an egg, we may turn to consider some- 

 what analogous tumours produced in the skin of 

 living animals. All have heard of the Breeze-fly 

 or Gad-fly of the ox (CEstrus bovis, Clark ; Hypo- 

 derma bovis, I>atr.) — a dipterous fly — termed, as 

 Virgil says, Asilus by the Romans, and CEstrus by the 

 Greeks ; and from his day to the present, notorious 

 as the terror of the hexd. 



The gadfly of the ox has tfce chest of a dark brown 

 colour, with a yellow patch on the back, and the 



V L. II. 



abdomen has alternate rings of black and yellow. 

 The appearance of this fly drives the cattle mad 

 with terror ; they utter loud bellowings, gallop over 

 the fields, 



"nnd scour the plain 

 In all the bright wverity of noon,'* 



exhausting themselves with efibrts to escape. 



The female of this insect is generally believed to 

 deposit her eggs in the fatty and cellular part of 

 the skin of cattle, by means of a singular ovi- 

 positor, consisting of a horny tube shutting up in 

 four pieces sliding within each other like a tele- 

 scope ; the terminal portion ends in five points, 

 which together constitute a borer. Of the five 

 points, three appear to be curved, the other two 

 are straight and shorter. By some the puncture with 

 this instrument is said to cause temporary but in- 

 tense pain, an acrid secretion being, it is supposed, 

 instilled into the wound ; and it is from an instinctive 

 dread of the suffering it produces, as they insist, that 

 the herd are scattered by the fly when it makes its 

 appearance. The QSstrus tarandi, however, is 

 an equal terror to the Reindeer, and according to 

 Linnaeus this fly lays its eggs merely on, not in, the 

 skin of that animal, the grub afterwards burrowing 

 its way and causing large tumours. 



Some naturalists consider that the puncture of 

 this fly does not occasion any pain, and that numbers 

 of eggs are deposited in places on the hide, from 

 which the ox could have lashed off' the insect with 

 its tail, and Reaumur says that he has seen an ox 

 flap away the ordinary flies collected upon a part 

 full of these tumours. 



On the contrary, Mr. Bracy Clark contends that 

 the gadfly does not pierce the skin with its ovipo- 

 sitor at all, but merely glues it to the hairs, and that 

 ai'terwards the grub eats its way under the skin, 

 causing swelling and suppuration. It is indeed dif- 

 ficult to decide between such conflicting opinions, 

 for it is almost impossible to bring the matter to the 

 test of personal observation. Reaumur, who supposes 

 a puncture, though without pain, to be made, says, 

 " Whenever I have succeeded in seeing these insects 

 at work, they have usually shown that they pro- 

 ceeded quite differently from what I had imagined, 

 but unfortunately I have never been able to see one 

 of them pierce the hide of a cow under my eyes." 

 If then the gadfly does not pierce the skin, or 

 pierces it without giving pain, to what are we to 

 attribute the terror of the herd ? The same query 

 equally applies to the terror displayed by the rein- 

 deer, of which Linnaeus says, that "though amongst 

 a herd of five hundred there were not above ten of 

 these flies, every one of the herd trembled and kept 

 pushing its neighbour about," and that " when the 

 fly touched any part of their bodies, they instantly 

 made efforts to shake it off'." It has been suggested 

 that the buzzing noise of the gadfly strikes the 

 cattle with instinctive terror, as the whirring noise 

 made by the rattlesnake does those animals liable to 

 the reptile's attack. 



Again, we are assured that the gadfly of the horse 

 (ffistrus equi) is beheld with every sign of agitation 

 by the latter, and assuredly that species deposits its 

 eggs on the hairs. 



Leaving then the question open as to whether the 

 gadfly of the ox makes a puncture or not, certain it 

 is that at a very early period the giubs are found 

 beneath the skin of the beast ; where they lie, tu- 

 mours, called warbles, form, and suppuration takes 

 place in the cellular tissue ; it is on the purulent 

 matter that the grubs feed, and as they grow, the 

 tumours become more extensive. Each grub is 

 thus as it were a tenant of a cell at once protecting 

 it and supplying it with nutriment. These tumours 

 have each an external orifice, and this is necessary 

 for the due respiration of the grub; its spiracles 

 are placed at the hinder part of the body, and the 

 position the grub occupies brings the tail to the 

 orifice, through which it emerges, rising to a level 

 with the external surface ; another object besides 

 the freedom of respiration is answered by this ori- 

 fice remaining open — it gives to the purulent matter 

 a free exit, and prevents the suppuration from ex- 

 tending to a dangerous degree. In due time the 

 grub has attained its full growth and is ready to as- 

 sume the pupa state ; it now pushes its way through 

 the orifice, and falling to the ground, burrows in the 

 earth, passes through a brief season of torpor, and 

 appears in August a winged gadfly, to continue its 

 progeny. Many of the grubs, however, perish; va- 

 rious birds watch their egress from the tumours, and 

 seize them as they are endeavouring to escape. The 

 jackdaw and magpie are expert at this service to 

 cattle; and the Pique Boeuf of Africa (see vol. i. p. 

 342) is of the same benefit to the large antelopes, 

 &c. 



Referring to our pictorial examples, Fig. 3511 re- 

 presents the ovipositor of the breezefly or gadfly 

 greatly magnified, with a hooked claw and part of 

 the tube still more enlarged. 



Fig. 3312 represents a the under surface of the 



grub of the Uistrus bovis ; b, the upper surface ; c, 

 the caudal extremity greatly magnified ; d, the tu- 

 mour or warble, with the tail of the grub appearing 

 at its external aperture. 



Fig. 3513 represents the fly, the pupa and grub 

 of the CEstrus bovis, with a magnified view of the 

 pupa. 



Fig. 3514 represents the tumours or warbles pro- 

 duced on the hide of cattle by the CEstrus bovis. 

 To these tumours the farmer pays too little alien- 

 tion ; the grubs are easily removed by pressure, and 

 it is certainly better to relieve a beast from their 

 annoyance than to sufter them to remain. 



The terrible zimb mentioned by Bruce in his tra- 

 vels, which lives during the grub state in the hide 

 of the elephant and rhinoceros, the ox and the camel, 

 appears to be related to the present species, but, if 

 Bruce is to be trusted, the zimb produces far more 

 formidable effects. 



MM. Humboldt and Bonpland discovered a spe- 

 cies in America, probably closely related to the 

 CEstrus bovis, which attacks man himself. The per- 

 fect insect is about as large as a housefly, and the 

 tumour formed by the grub is generally in some part 

 of the abdominal region ; the grub requires six 

 months to come to maturity, and if irritated is apt 

 to work its way deeper into the flesh, and thus 

 sometimes occasions fatal inflammation. 



With respect to the CEstrus equi, or horse gadfly, 

 it glues by means of its ovipositor its eggs on the 

 hair of the horse, instinctively selecting some part 

 which it can reach to lick with its tongue ; and, 

 after depositing her store to the number of fifty or 

 a hundred, soon perishes. These eggs may be seen 

 about the shoulders and legs of horses turned out 

 to grass in August. Two or three days after being 

 deposited they are ready to be hatched. Possibly 

 the horse feels a little inconvenience from all this 

 glutinous matter sticking about and stiffening the 

 hair, and he licks the part, and by the pressure of 

 the tongue, and the mingled influence of the warmth 

 and moisture of it, the ova are burst, and a small 

 worm escapes from each. It clings to the tongue, 

 and is thus conveyed info the mouth ; thence it is 

 either carried with the food into the stomach, or, 

 impelled by instinct, it travels down the gullet, 

 being of too tiny size to inconvenience or annoy 

 the horse. Thus it reaches the stomach, and, by 

 means of a hook en each side of its mouth, affixes 

 itself to the cuticular or insensible coat of that vis- 

 cus, into which its muzzle is plunged ; there it re- 

 mains until the early part of the summer of the fol- 

 lowing year, feeding on the mucous or other matter 

 which the coats of the stomach aff'ord. It has now 

 become an inch in length and of corresponding 

 bulk, and ready to undergo its change of form. It 

 detaches itself from the cuticular coat to which it 

 had adhered, and plunges into the food which the 

 other and digestive poifion of the stomach contains ; 

 it passes with the food through the whole length of 

 the intestines, and is discharged with the dung. It 

 then hastens to burrow into the earth, and, if it has 

 escaped the birds that are eagerly watching for it, it 

 has no sooner hollowed for itself a convenient habi- 

 tation than a shelly covering is formed around it, 

 and it appears in the state of a pupa or chrysalis. 



It here lies torpid lor a few weeks, preparing to 

 undergo its last change. It assumes the form of a 

 perfect fly ; it then bursts from its prison, rises in 

 the air, and seeks its mate. The work of fecunda- 

 tion being accomplished, the male immediately dies: 

 the female lingers a day or two in order to find the 

 proper deposit for her eggs, and her short life also 

 terminates. 



The numbers of these larv;e or hots with which 

 the stomach of the horse is sometimes crowded are 

 almost incredible ; we have seen large patches of 

 them in close array ; they occupy the cardiac portion, 

 and are said, formidable as they seem, to produce 

 no mischief; at least such instances are rare and 

 accidental, other causes combining with their pre- 

 sence. Occasionally they have fastened about the 

 larynx, and produced a distressing cough, which no 

 medicine could alleviate, and which became more 

 and more aggravated as the larvae increased, lill the 

 suff'erer sank under the exhaustion produced by 

 incessant irritation. 



Fig. 3515 represents— A, the female of the CEstrus 

 equi, nearly twice the natural size : B, two eggs 

 magnified, deposited on a hair ; C, bots, one half 

 their natural size, adhering by their tentacular months 

 to the cuticular portion of the stomach. Excava- 

 tions are seen in the cuticular coat, showing where 

 others had been recently fixed ; D, the full-grown 

 hot detached ; E, the Gadfly of the sheep (CEstrus 

 ovis). The latter fly lays her eggs on the inner 

 margin of the nostril of the sheep, and the larvae 

 creep up the nostril, threading the sinuosities of the 

 way, and causing the most dreadful irritation, which 

 almost maddens the poor animal ; ultimately they 

 reach the frontal sinuses, and fasten themselves on 

 the living membrane, fiom whicli when fully grown 

 they detach themselves and creep down asain, and 



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