A WAIRARAPA "YET." ON THE BOT FLY.

Otago Witness, Issue 2085, 8 February 1894, Page 11

A WAIRARAPA "YET." ON THE BOT FLY.

That the bot fly has made its appearance in the Wairarapa this summer is not to be denied, but from certain specimens of ova, &c, which have been brought to me within the last few days I am of the opinion that many owners of horses are labouring under a delusion as regards the species of fly generally worrying their animals. With a view to enabling everyone interested in the matter to discover for himself the nature of the different bots, I shall devote a short space to a description of the three known species of the fly, and trust that by so doing the doubt constantly arising re this question may be set at rest.

The first one I have to deal with is the CEstrus equi, or large spotted horse bot — the most interesting of the three. When the female has been impregnated, and the eggs sufficiently matured, she Eeeks among the horses a subject for her purpose, and, approaching him on the wing, she carries her body nearly upright in the air, and her tail, which is lengthened for the purpose, curved inwards and upwards. She suddenly darts upon the horse (generally upon the inner side of the foreleg), and instantly deposits her eggs. The back of the shoulders and extreme ends of the hairs of the mane are also favourite spots.

Now the common notion is that the eggs are licked off the skin and carried into the stomach, but I do not find this to be the case always— it may be accidental, for when they have remained on the hair four or five days they become ripe, after which time slightest application of warmth and moisture is sufficient to bring forth in an instant the latent larvrc. At this time if the t-ngue of the horse touches the egg its operculum is thrown open, and a small, active worm is produced, which readily adheres to the moist surface of the tongue, and is from thence conveyed with the food into the stomash. The larva or worm, being hatched in the stomach, immediately clings by means of its tentaculce— two dark brown hooks between which is its mouth— to the cutieular coat, which they pierce, though they never insinuate their points into the muscular or sensitive tunic beyond it. In this manner so pertinaciously does the bot adhere that in my attempts to unhitch it it frequently suffered its hooks to be broken, or even its body severed, rather than quit its hold. Now and then, but I believe very rarely, they are found hooked in the villous coat. These, however, are nothing more than stragglera— bots, probably, that had on their arrival in the stomach been hastily carried with the aliment into its vascular part before they had the power of fixing their hooks into the cuticular. The apprehensions of persons as to the pain caused by these insects ought from this to be stifled, for how can they possibly irritate when fastened to an insensible part — a part as devoid of feeling itself as the very hoofs are ? Not infrequently I have found bots in the duodenum, and on some occasions, more have appeared in the vascular than the cuticular portion of tho stomach, and this is in the month of January, their ordinary and natural nidus being the cuticular pouch of the stomach. Again, I have discovered them in the esophagus. The bot remains in the stomach of the horse throughout the winter until the spring, when, being at the consummation of this stage or form of existence, it spontaneously disengages itself, and passes with the chymous matters into the intestinal canal, where its stay, as a natural consequence, is short, it being cast out with the dung. It is about the beginning of our summer that our farmers, for the first time, see that their horses are suffering from what is generally known as worms. If, however, these people will have patience, the imaginary plagues will spon quit the bowels of their horses of their own accord, the time being now arrived for them to take on other forms, and answer all the remaining ends of nature. The larva, being ejected, lies not long exposed on the ground, but quickly dries up into a state of chrysalis or grub, in which condition it remains for a few weeks, when, parts of th 9 future insect being hardened, and superfluous moisture all gone, it bursts, and the fly makes its exit at the small end. In a few hours these flies are prepared to seek mates, and then search among the horses for proper subjects for their purposes. A far more annoying insect to the horse than the CEstrus equi is the fundament bot (CEstms hemorrhoidalis), whose manner of depositing eggs is similar to the other, but the parts it chooses for the purpose are the lips and corners of the mouth, which is very distressing to the horse on account of the excessive titillation it causes. Immediately after the fly has touched him the horse rubs his mouth against his forelegs and the ground, or sometimes against a tree, with great emotion, till at length, finding this means of defence insufficient, he gallops away to the nearest water, where, strange to say, the costrus never follows him. These flies hide in the grass, and as the hor&e stoops to feed they dart upon him, always poising themselves, as has been described, before depositing their eggs. The larvae or grubs of this species inhabit the stomach in the same way as the equi, generally adhering to the white lining, and are disposed promiscuously in dense clusters after the same manner. They may, however, be distinguished by being in general smaller, longer in proportion to their bulk, and rounder, and of a duller red— more inclining to white. These bots remain in the stomach the same length of time as the equi ; but instead of being cast out, they stick more or less within the verge of the anus, adhering to its soft lining, and producing excessive and constant irritation, thus making the horse lazy, unwilling, and awkward. A sure sign that a horse is suffering from the fundamental bot is when he rubs his breech against any obstacle at hand. The red bot vetorinus) is less known than the former two, as far as its habits are concerned. There is no doubt, though, that they deposit their egg* upon the lips of the horses, and cause considerable pain by stinging. The larvre of this species may be recognised by "its smaller size and tapering oblong figure, and the segments are more detached and rounded, shining, smooth, and of a pellucid red or ruby colour, more particularly at the tail or obtuse end."

In the opinion of many experts, bols exert a salubrious effect on the stomachs of horses by promoting digestion, or acting as what are called vellicatories, the local stimulants and detractors, on the principles of counter-irrita-tion. With this, however, I cannot agree. It must not be forgotten that bots are attached to a part of the stomach that does not perform any proper digestive function, and that all stimulants and other substances promotive of digestion must be applied to the vascular part, the only veritably digestive surface, or it is obvious they can have no such effect. Indeed I do not see how bots can perform the office of stimuli at all, unless it be that bj some motion they are capable of they may have any such influence upon the mucous follicles — placed in abundance under the cuticular coat ; but then, again, it has not been absolutely proved that this secretion is necessary to digestion. As long as bots exist in a small number they do no harm and cause no pain, but in a multitude they occasion sharp pains, and prove

detrimental to digestion by absorbing the greater part of the juices necessary for that operation. I have recently examined horses after death, and found the lining membrane in a state of mortification. In one case there were 40 red bots in the stomach, which had in places almost eaten through its coat. Again, in another animal I came across a large number of white bots in the esophagus, the cuticular coat being eaten through. It will be seen from the foregoing that, unless present in large numbers, the bot is not injurious to horses. With the many preventives and cures suggested I have nothing to do now, my motive being merely to place before the public the results of my experiments upon subjects infected with the disease. All horses which are run to grass are subject to bots, but it is a difficult matter indeed for a veterinary surgeon to tell whether a horse is suffering pain from them or from colic. How easy, then, must it be for an inexperienced person to come to a wrong conclusion upon the matter ? In fact, in most cases where my services have been required I have found that the pains attributed to bots by horseowners were caused by nothing else but colic — C. W. Langstone, M.R.C.V.S., in the Wellington Post.