1S37] 



FARMERS' REGISTER. 



4/57 



From tlie Aiiit'ricnn 'I'uif Register. 

 OESTRUS KQUI — BOTS OR GRUBS. 



Hanover, Va. March 10, 1833. 



iMr. Kditor: As I think it probabl*^ that much 

 mischief is altribuied to the hots or grubs, which, 

 if correctly understood, would be justly ascribable 

 to olher causes, I have thouo-ht the Ibllowiuir nc- 

 couiil ol' that insect, its production, and the circum- 

 stances of its existence, might not be unacceptable 

 to the public. 



The bofs are the larvtp of a fly known to nat- 

 uralists as belouijiuu to the family ol'the oestrus or 

 gadfly, and is called in natural history oestrus equi, 

 and more extensively known to tlie people of this 

 country under the vulgar denomination of the nit 

 fly. The oestrus cqui makes its appearance, in 

 our climate, from the latter part of July to the mid- 

 dle of August. The female becomes impregna- 

 ted very soon after her escape from the chrysalis, 

 and soon begins to deposite her eggs, which she 

 continues to do from that time to the end of au- 

 tumn, when she falls a victim to the chills of the 

 season. It requires but little talent for observation 

 to discover that this fly, on her arrival in a field 

 where there are several horses, soon manifests a 

 preference for some one of them, and attaches her- 

 eelf to this one with so much constancy, that 

 though she irtay be driven off repeatedly, she will 

 still pertinaciously return, though she may iiave 

 uninterrupted access to others. It is impossible to 

 point out withcertainty the circumstances on which 

 this preference depends. Whether the oestrus 

 possesses the instinctive fiiculty of discovering cer- 

 tain marks of cutaneous irritation about one ani- 

 mal, which renders him more disposed to bite and 

 pinch at the integuments with his inouth than an- 

 other, and thereby more certain to give her egirs a 

 conveyance to the future nidus of the larva-; or 

 whether she observes that the hair on one horse is 

 arranged in a manner that renders it more easy of 

 access for the deposite of her eggs than that of an- 

 other; or lastly, whether her attachment depends 

 on the iTiore or less patient civility with which dil- 

 ferent horses receive her buzzing addresses, must 

 be left tor the determination of the sajracious read- 

 er. The fact, however is so; and the insect hav- 

 ing fixed on the object of her choice, commences 

 immediately the deposite of her ejjgs in the fol- 

 lowing manner, which no doubt is periectly famil- 

 iar to most of your readers. 



Having poised herself in the air in the vicinity 

 of the part on which she inliMids to deposite the 

 ^S^''' (and this is most generally about the knee, 

 the inside of the fore leg, the rear of the shoulder, 

 and more rarely on the mane,) with her head ele- 

 vated, her body in nearly an erect position, and 

 her long and slender tail curved inwards and up- 

 wards in a manner that brings it nearly in contact 

 with the erect abdomen, she every now and then 

 darts at the subject with great quickness, at the I 

 same time suddenly throwing her tubular tail from I 

 its approximation to her body, so as to form a riiiht { 

 angle with her erect position, and shooting forth 

 the egg from its capsule, (by means of certain | 

 muscles that perform that ofTice,) it is attached to 

 a single hair, (which she strikes with unerring 

 certainty,) by a glutinous fiuid, which also answers 

 the purpose of lubricating its exit from the viscu.s 

 containing it, and when dry, of confining it firmly 

 to its new situation. The egg thus deposited has 

 Vol. V-58 



been supposed by the unobservant to be licked or 

 pinched ofl occasionally by the animal, and swal- 

 lowed with the hair to which it is attached., and 

 hatched in the stomach. A little reflection, how- 

 ever, would satisly us of the improbability of' this : 

 lor the inanimate egg would most probably blend 

 with the food, and pass oil' with the excremenii- 

 (ious substances from the bowels, without hatch- 

 ing; thereby li'uslrating the object ol nature in the 

 whole arrangement. 



Mr. Clark has discovered, and communicated 

 to the LinniPii .Society, among other interesting 

 facts in respect to the oestrus, that the egg becotnci>i 

 ripe lor aniinalization in (bur or five days from it.i 

 deposite, and thai at its highest state of maturity 

 it is almost instantly quickened on meeting with 

 warmth and moisture. There can be no doubt, 

 therefore, that the egg, if received into the mouth, 

 or even licked with the tongue, at this auspicious 

 period, is instantly hatched, and that the small lar- 

 va, ejected fi'om its operculum, readily attaches it- 

 self to the parts about the mouth and fiiuces, and 

 is either carried to the stomach with the saliva, or 

 with the water or food in their passage thither, 

 where it soon attaches itself to the villi of its inner 

 coat by means of two hooks or tenfacula; one of 

 which is situated on each side of the longitudmal 

 aperture, through which the larva? evidently re- 

 ceive their fijod. Hooked in this manner to the 

 inner coat of the stomach, its residence may be 

 considered fixed: for I imagine these larvit never 

 leave the situation they chance at first to occupy 

 in the stomach of the horse till they arrive at the 

 insensible state of the chrysalis, when they drop 

 off as a matter of necessity, just as ripe fruit drops 

 from the tree. Loosened from its hold on the villi 

 of the stomach, it soon blends with the contents 

 of that organ, passes into the bowels, and is eject- 

 ed with the excrementitious matter. Incapable of 

 locomotion, it is now dependent on chance for its 

 future destinies. Should it happen to be thrown 

 into the dunghill, along with the excrementa with 

 which it was voided — or should it be dropped 

 amongst thick luxuriant herbage, or in the thickest 

 grass of some rich pasture, where it will remain 

 undisturbed, under the protection of the alvine de- 

 posite made at the time of its ejection, it will, in 

 the course of three or four weeks, produce the per- 

 led oestrus or gad fly, capable of reproducing its 

 species. Happily, however, for the animal whose 

 stomach itinlests, tiut few of the hundreds of eggs 

 that are deposited on a single horse arrive at this 

 state of consummated existence. A variety of 

 hazards await 1;hem through all the various stages 

 and circumstances of their progress frnrn this state 

 to that of the fly. Such is their fecundity, when 

 fully matured, that the slightest touch of warmth 

 and moisture causes the little flBtus to burst 

 through its prison; and should that warmth and 

 moisture chance to proceed from a light shower, 

 under the genial influence of the autumnal sun, in- 

 stead of the lips or tongue of the animal, it falls to 

 the ground and perishes. Should the little larva 

 arrive safely in the horse's mouth, it has there to 

 pass through the lottery of the teeth, and incur the 

 hazards ol' mastication: and even should it draiv a 

 prize, and pass safely from this situation to the 

 stomach, enveloped here in the huge mass of in- 

 gesta, there are great odds in favor of its passing 

 on to the bowels, where, subjected to the action 

 of the bile, it generally prefers a premature death 



