THE SHEEP NOSTRIL FLY.

Otago Witness, Issue 2652, 11 January 1905, Page 6

THE SHEEP NOSTRIL FLY.

In the last of her reports on injurious insects and common farm pests, the late Miss E. A. Ormerod devoted a special chapter to the sheep nostril fly, an insect which causes more annoyance and irritation to sheep and .much greater- loss to flock masters than is generally supposed. The fly is. known to entomologists by the name of (Estrus ovis, and measures from two.fifths of an inch to half an inch in length. Its method of attack is to deposit its larva -r maggot on or just within the opening of the sheep's nostrils. From this point the maggot begins to at once make its way upwards on the inside of the nostril by means of hooks and spines with which it iis fumisned. At this stage of its growth the maggot is but a very tiny creature, only aoout one-twelfth of an inch in length. After starting on its journey inside the sheep's nostril, the maggot progresses upwards by fixing its hooks in the mucous membrane until it reaches the furthest chambers or recesses of the nose. There it attaches itself to the flesh and goes on feeding until it has reached maturity. When they arrive at this stage they loosen their hold of the lining membrane and drop to the ground, but sometimes they are expelled by being sneezed out. The season of the year at which they are most noticed is from, the spring to the approach of the autumn (in England from the middle ji April to the end of July), and it is during, that period that they usually leave the nostrils, but they may also be found present at other times and at various stages of development. There is some difference of opinion as to how long they remain in the nostrils, -ome writers have stated that they remain there for about ten months, but according to Miss Ormerod this has not been "definitely proved^ After the maggot escapes from the nostril and falls- to the ground, it bores down into the earth for an , inch or twtf, and there changes to a chrysalis of a dark-brown colour, within w-hich the fly develops, and from which it emerges in due course. The exact length of time it takes the fly to develop is a matter about which there is some difference of opinion. Some authorities hold that it develops in from three to four weeks, while others contend that it requires fully twice that time in order to reach its full development. Its rate of growth as, however, largely dependent upon the nature of the weather. As a rule, attacks of this nostril fly are not productive of serious consequences, though Professor M'Fadyean states that one year very serious losses among sheep werecaused by the parasite in Wales. Sometimes there is a good deal of trouble, amounting in severe cases to difficulty of breathing, from stoppages occasioned by the presence of the maggots or inflammation of the mucous membrane, but excepting (as above mentioned) where there are many maggots, the attack does not appear to be often fatal, and when the cause of the trouble is got rid of in natural course, the sheep recovers. The presence of the nostril fly in a flock <may be known by the sheep holding their noses close to the ground, shaking their heads, and striking the ground violently with- their forefeet. At times, when tfie fly is about, the animals will gather together with their heads in the centre, and their noses down to the ground and buried in dust or sand If there is any. Occasionally, too, one sheep will be' seen going off at a gallop, as if to escape from an enemy.

In regard to localities in which the maggot may be found, the idea winch at one time was prevalent that it is to Be found in the brain itself has been entirely disproved by modern investigators. One special sign of the presence of the maggot in an advanced stage of the attack is a catarrhal discharge from the nose, whicu is stated to be at first clear and serous, then thick and mucous. Frequently there is sneezing and snorting, from time to time the animals stagger and are seized with vertigo, but do not turn in a circle. In severer cases there is difficulty of breathing, the first respiratory passages being obstructed by the larvas or the inflammation of the mucous membrane. Tha fact of the nostril-maggot-infested sheep not turning in a circle is one very important point whereby to distinguish this attack from the so-called "gid," or staggers, produced by presence of the hydatid Ccenurus cerebralis (the early stage of the tapeworm of the dog), in which the affected sheep does turn, but lias not the symptoms of nasal discharge or snorting.

Where maggot presence is found only on one side of the nose, the operation of trephining is sometimes performed with the object of curing the animal. An opening is made with an Instrument called a trephine into the frontal sinus (one of tie passages to which the maggots can creep from the lower part of the nostrils), and through this opening some of the maggots may be observable and may He picked out with forceps. To kill others, benzine diluted with water has Been used. But the operation i§ tedious^ requires some skilly

and should only be performed by a veterinary surgeon, while the ultimate results are not such as to make the opera tion what can be generally advised. For available and serviceable treatment, a practical means of prevention consists in smearing the noses with a mixture of equal parts of tar and grease, or of tar and fish oil or jf tar and whale oil. The better way is to apply the preparation directly with a brush. Some recommend smearing the salt and grain troughs from which the animals feed with the mixture, expecting the sheep whilst feeding to get more or less on the nose. This method is not trorough enough. The following ointment is recommended as a good dressing for preventing the flies from laying their eggs on the nostrils of the sheep : — Linseed oil 1 pint Beeswax IM2 Carbolic acid 4oz In order to prepare this ointment mix the wax and oil togetner, adding 2oz of resin to give body ; then, as it is cooling, stir in the' carbolic acid. This dressing should be rubbed over the face and nos» every two or three days during, say, .a month of the weather in which the flies threaten attack. Probably the tar and whale oil preventive will prove preferable, as it is equally effective and fewer smearings will be found necessary.