78 LETTER V. INJURIES CAUSED BY INSECTS. INDIRECT INJURIES, HAVING detailed to you the direct injuries which we suffer from insects, I am now to call your attention to their indirect attacks upon us, or the injury which they do our property; and under this view also you will own, with the fullest conviction, that they are not beings that can with prudence or safety be disregarded or despised. Our property, at least that part exposed to the annoyance of these creatures, may be regarded as consisting of animal and vegetable productions, and that in two states; when they are living, namely, and after they are dead. I shall therefore endeavour to give you a sketch of the mischief which they occasion, first to our living animal property, then to our living vegetable property; and, lastly, to our dead stock, whether animal or vegetable. Next to our own persons, the animals which we employ in our business or pleasures, or fatten for food, individually considered, are the most valuable part of our possessions and at certain seasons, hosts of insects of various kinds are incessant in their assaults upon most of them.-To begin with that noble animal the horse. See him, when turned out to his pasture, unable to touch a morsel of the food he has earned by his labours. He flies to the shade, evidently in great uneasiness, where he stands continually stamping from the pain produced by the insertion of the weapons sheathed in the proboscis of a little fly (Stomoxys calcitrans) before noticed as attacking ourselves. This alights upon him sometimes in one place and sometimes in another, and never lets him rest while the day lasts. See him again when in harness and travelling. He is bathed in blood flowing from innumerable wounds made by the knives and lancets of various horse-flies (Tabanus L.), which assail him as he goes, and allow him no respite2; and consider that even this is nothing to what he suffers in other climates from the same pest. In North America, vast clouds of different speciesso abundant as to obscure every distant object, and so severe in their bite as to merit the appellation of burning flies-cover and torment the horses to such a degree as to excite compassion even in the hearts of the packhorsemen. Some of them are nearly as big as humble-bees; and, when they pierce the skin and veins of the unhappy beast, make so large an orifice that, besides what they suck, the blood flows down its neck, sides, and shoulders in large drops like tears, till, to use Bartram's expression, "they are all in a gore of blood." Both the dog-tick and the American tick before mentioned, especially the latter, also infest the horse. Kalm affirms, that he has seen the under parts of the belly, and other places of the body, 1 See above, p. 25. 2 Once travelling through Cambridgeshire with a brother entomologist in a gig, our horse was in the condition here described, from the attack of Tabanus rusticus. so covered by them, that he could not introduce the point of a knife between them. They were deeply buried in the flesh; and in one instance that he witnessed, the miserable creature was so exhausted by continual suction, that it fell, and afterwards died in great agonies.1 No quadruped is more infested by the gad- or bot-fly, sometimes also improperly called the breese, than the horse. In this country no fewer than three species attack it. The most common sort, known by the name of the horse-bee (Estrus Equi), deposits its eggs (which being covered with a slimy substance adhere to the hairs) on such parts of the body as the animal can reach with its tongue; and thus, unconscious of what it is doing, it unwarily introduces into its own citadel the troops of its enemy. Another species (E. hæmorrhoidalis) is still more troublesome to it, ovipositing upon the lips; and in its endeavours to effect this, from the excessive titillation it occasions, giving the poor beast the most distressing uneasiness. At the sight of this fly horses are always much agitated, tossing their heads about in the air to drive it away; and, if this does not answer, galloping off to a distant part of their pasture, and, as their last resource, taking refuge in the water, where the gad-flies never follow them. We learn from Reaumur, that in France the grooms, when they observe any bots (which is the vulgar name for the larvæ and pupa of these flies) about the anus of a horse or in its dung, thrust their hand into the passage to search for more; but this seems a useless precaution, which must occasion the animal great pain to answer no good end; for when the bots are passing through the body, having ceased feeding, they can do no further injury. In Sweden, as De Geer informs us, they act much more sensibly: those that have the care of horses are accustomed to clean their mouths and throats with a particular kind of brush, by which method they free them from these disagreeable inmates before they have got into the stomach, or can be at all prejudicial to them.3 Providence has doubtless created these animals to answer some beneficial purpose; and Mr. Clark's judicious conjectures are an index which points to the very kind of good our cattle may derive from them, as acting the part of perpetual stimuli or blisters: yet when they exceed certain limits, as is often the case with similar animals employed for purposes equally beneficial, they become certainly the causes of disease, and sometimes of death. How troublesome and teasing is that cloud of flies (Anthomyia meteorica) which you must often have noticed in your summer rides hovering round the head and neck of your horse, accompanying him as he goes, and causing a perpetual tossing of the former! - And still more annoying in Lapland, as we learn from Linné5, is the furious assault of the minute horsegnat (Culex equinus L.), which infests these beasts in infinite numbers, running under the mane and amongst the hair, and piercing the skin to suck their blood. An insect of the same genus is related to attack them in a particular district in India in so tremendous a manner as to cause in 1 De Geer, vii. 158. 2 See Mr. W. S. MacLeay in Linn. Trans. xiv. 355. 3 De Geer, vi. 295. 5 Linn. Flor. Lapp. 376. Lach. Lapp. i. 233, 234. 4 Aman. Acad. iii. 358. This insect from Linné's description is probably no Culex, but perhaps a Simulium Latr. (Simulia Meig.) curable cancers, which finally destroy them.1-But of all the insect tormentors of these useful creatures, there is none more trying to them than the forest-fly (Hippobosca equina). Attaching themselves to the parts least covered with hair, particularly under the belly between the hind legs, they irritate the quietest horse, and make him kick so as often to hazard the safety of his rider or driver. This singular animal runs sideways or backwards like a crab; and, being furnished with an unusual number of claws, it adheres so firmly that it is not easy to take it off; and even if you succeed in this, its substance is so hard, that by the utmost pressure of your finger and thumb it is difficult to kill it; and if you let it go with life, it will immediately return to the charge. Amongst the insect plagues of horses, I should also have enumerated the larva of Lixus paraplecticus, which Linné considers as the cause of the equine disease called in Sweden, after the Phellandrium aquaticum, "Stákra," had not the observations of the accurate De Geer rendered it doubtful whether the insect be at all connected with this malady." Another quadruped contributing greatly to our domestic comfort, from which we derive a considerable portion of our animal food, and which, on account of its patient and laborious character when employed in agriculture, is an excellent substitute for the horse (you will directly perceive I am speaking of the or, whether male or female), is also not exempt from insect domination. At certain seasons the whole terrified herd, with their tails in the air, or turned upon their backs, or stiffly stretched out in the direction of the spine, gallop about their pastures, making the country reecho with their lowings, and finding no rest till they get into the water. Their appearance and motions are at this time so grotesque, clumsy, and seemingly unnatural, that we are tempted rather to laugh at the poor beasts than to pity them, though evidently in a situation of great terror and distress. The cause of all this agitation and restlessness is a small gad- or bot-fly (E. Bovis) less than the horse-bee, the object of which, though it be not to bite them, but merely to oviposit in their hides, is not put into execution without giving them considerable pain. When oxen are employed in agriculture, the attack of this fly is often attended with great danger, since they then become perfectly unmanageable; and, whether in harness or yoked to the plough, will run directly forward. At the season when it infests them, close attention should be paid, and their harness so constructed that they may easily be let loose. Reaumur has minutely described the ovipositor, or singular organ by which these insects are enabled to bore a round hole in the skin of the animal and deposit their eggs in the wound. The anus of the female is furnished with a tube of a corneous substance, consisting of four pieces, which, like the pieces of a telescope, are retractile within each other. The last of these terminates in five points, three of which are longer than the others, and hooked: when united together they form an instrument very much like an auger or gimlet; only, having these points, it can bite with more effect. He thinks the infliction of the wound is not attended by much pain, except where very sensible nerves are injured, when the 1 Life of General Thomas, 186. 2 Linn. It. Scand. 182. De Geer, v. 227-230. 3 Mr. Clark, however, is of opinion that the gad-fly does not pierce the skin of the animal, but only glues its eggs to it; the young larvæ when hatched burrowed into the flesh. Essay on the Bots of Horses and other Animals, p. 47. animal, appearing to be seized with a kind of frenzy, begins to gambol, and run with such swiftness that nothing can stop it. From this semblance of temporary madness in oxen when pursued and bored by the Estrus, the Greeks applied the term to any sudden fit of fury or violent impulse in the human species, calling such ebullition an Estrus. The female fly is observed to be very expeditious in oviposition, not more than a few seconds; and while she is performing the operation, the animal attempts to lash her off, as it does other flies, with its tail. The circular hole, made by the augur just described, always continues open, and increases in diameter as the larva increases in size; thus enabling it to receive a sufficient supply of air by means of its anal respiratory plates, which are usually near the orifice.—But though these insects thus torment and terrify our cattle, they do them no material injury. Indeed, they occasion considerable tumours under the skin, where the bots reside, varying in number from three or four to thirty or forty; but these seem unattended by any pain, and are so far from being injurious, that they are rather regarded as proofs of the goodness of the animal, since these flies only attack young and healthy subjects. The tanners also prefer those hides that have the greatest number of bot-holes in them, which are always the best and strongest.1 The Stomoxys, and several of the other flies before enumerated, as well as the dog and American ticks, are as prejudicial to the ox as to the horse. One species of Hippobosca, I have reason to believe, is appropriated to them; yet, since a single specimen only has hitherto been taken, little can be said with respect to it.-A worse pest than any hitherto enumerated is a minute fly, concerning the genus of which there is some doubt, Fabricius considering it as a Rhagio (R. columbaschensis) and Latreille as a Simulium; but to whatever genus it may belong, it is certainly a most destructive little creature. In Servia and the Bannat it attacks the cattle in infinite numbers, penetrates, according to Fabricius, their generative organs, but according to other accounts their nose and ears, and by its poisonous bite destroys them in the short space of four or five hours. Much injury was sustained in 1813 from this insect in the palatinate of Arad, in Hungary, and in the Bannat; in Banlack not fewer than two hundred horned cattle perishing from its attacks, and in Versetz, five hundred. It appears towards the latter end of April or beginning of May in such indescribable swarms as to resemble clouds, proceeding, as some think, from the region of Mehadia, but according to others from Turkey. Its approach is the signal for universal alarm. The cattle fly from their pastures; and the herdsman hastens to shut up his cows in the house, or, when at a distance from home, to kindle fires, the smoke of which is found to drive off this terrible assailant. Of this the cattle are sensible, 1 Much of the information here collected is taken from Reaum. iv. Mem. 12.; and Clark in Linn. Trans. iii. 289. 2 The writer of the present letter is possessor of this specimen, which he took on himself in a field where oxen were feeding. 3 In the Systema Antliatorum (p. 56.) Fabricius most strangely considers thi insect as synonymous with Culex reptans L., calling it Scatopse reptans, and dropping his former reference to Pallas, and account of its injurious properties. Meigen (Dipt. i. 294.) makes this insect a Simulia, under the name of S. maculata. It is represented by Coquebert, whose figure is copied in the translation of Köllar's work referred to above, and also in the next page. G and as soon as attacked run towards the smoke, and are generally preserved by it.1 Tabani in this country do not seem to annoy our oxen so much as they do our horses; perhaps for this immunity they may be indebted to the thickness of their hides; but Virgil's beautiful description of the annoyance shows that the Grecian Estrus, called by the Romans Asilus, evidently is one of the Tabanide. As the passage has not been very correctly translated, I shall turn poet on the occasion, and attempt to give it you in a new dress. Through waving groves where Selo's torrent flows, (Estrus in Greece, Asilus named at Rome,) Their lowings shake the woods and shake the sky, In some parts of Africa also insects of this tribe do incredible mischief. What would you think, should you be told that one species of fly drives both inhabitants and their cattle from a whole district? Yet the terrible Tsaltsalya or Zimb of Bruce (and the world seems now disposed to give more credit to the accounts of that traveller) has power to produce such an effect. This fly, which is a native of Abyssinia, both from its habits and the figure appears to belong to the Tabanide, and perhaps is congenerous with the Estrus of the Greeks.2 1 Fabr. Ent. Syst. Em. iv. 276. 22. Latr. Hist. Nat. &c. xiv. 283. Leips. Zeit. July 5. 1813, quoted in Germar's Mag. der Ent. ii. 185. In Köllar's Treatise on Insects injurious to Gardeners, Foresters, and Farmers (Lond. 1840), a valuable work, for a translation of which from the German into English we are indebted to the Misses Loudon, it is stated (p. 70.) that Dr. Schönbauer, late Professor of Natural History at Pesth, has ascertained that the swarms of this fly, which he calls Simulia Columbaschensis, instead of proceeding, as the Wallachians universally believe, from the jaws of the dragon killed by St. George, and buried in certain caves in the limestone mountains near Columbaez in Servia, out of the mouths of which they issue like smoke, in fact are bred in the extensive swamps in the district, passing all their states of egg, larva, and nymph in water. Vast swarms appeared in 1830 in a large tract of Austria, Hungary, and Moravia, overflowed by the river Marsch, and hundreds of horses, cows, and swine perished from their bite. Men are equally attacked by this scourge, but can more easily defend themselves; and there are not wanting solitary examples of little children dying from the excessive inflammation consequent on their numerous punctures. 2 It is by no means clear that the Estrus of modern entomologists is synonymous with the insects which the Greeks distinguish by that name. Aristotle not only describes these as blood-suckers (Hist. Animal. 1. viii. c. 11.), but also as furnished with a strong proboscis (1. iv. c. 7.) He observes likewise that they are produced from an animal inhabiting the waters, in the vicinity of which they most abound (1. viii. c. 7.). And Elian (Hist. 1. vi. c. 38.) gives nearly the same account. Comparing the Estrus with the Myops (synonymous perhaps with Tabanus Latr., except that Aristotle affirms that its larvæ live in wood, 1. v. c. 19.), he says, the Estrus for a fly is one of the largest; it has a stiff and large sting (meaning a proboscis), and emits a certain humming and harsh sound; but the Myops is like the Cynomyia— it hums more loudly than the Estrus, though it has a smaller sting. These characters and circumstances do not at all agree with the modern Estrus, which, so far from being a blood-sucker furnished with a strong proboscis, |