The FARM

North Canterbury Gazette, Volume 6, Issue 65, 6 April 1937, Page 6

The FARM

THE NOSTRIL FLY

Bot That Troubles Sheep TARRED SALT BOXES AS PRECAUTION (By “YET.” in an exchange from England.) Like other - members of the bot fly family, the sheep nostril fly (oestrus ovis) causes the greatest harm during the larval, or maggot, stage, which it passes in the nasal chambers and face sinuses of the sheep. It is a somewhat hairy fly, about half an inch long, with glassy looking wings that extend beyond the body when the fly is at rest. The top of its head is light brown in colour, and that of the fore-part of the body or thorax brown or yellow to grey; the abdomen is brownish yellow with dark spots, and the legs are brown. Worst in Hot Weather The flies are more active during warm sunny weather, and after mating the female deposits her eggs, or sometimes living larvae, in the nostrils of the sheep. The larvae are provided with hooks and spines by which they crawl up the nostrils and nasal chambers and finally reach the sinuses of the face and head. During this migration, they set up a very considerable irritation of the mucus membranes by their presence and prickings, which results in a great increase of tho nasal secretions. Life History The maggots" remain in the sinuses until they become mature and then make their way back to the nasal chambers, from which they are sneezed out on to the ground. They then hide themselves under a tuft of grass, or a little below the surface of the ground, and pass into the chrysalis form. In due course the fly emerges from the pupal case or chrysalis, the whole cycle from egg to fly having taken about 10 months.

As the flies do not sting it is rather remarkable that sheep show such fear of them. The same fear is, however, manifested both by cattle and horses when their own particular hot flies are about, so it really seems that some instinct warns animals of what may be in store for them, should the fly strike. In their efforts to escape, sheep will rush about holding their noses close to the ground, or rubbing them into the dust, to hamper the fly as much as possible. The discharge from the nose differs somewhat from that seen in ordinary colds or bronchitis, in that it is very sticky and tends to gum up the nostrils. The sheep are continually sneezing in their efforts To get rid of the maggots; they toss their heads about, and rub their noses along the ground.

Sometimes they walk with a high stepping gait, with the head held high in the air, and one might mistake the case for one of gid were it not for the discharge from the nose. A Counsel op Perfection When a pasture is known to be infested by the fly, sheep should be kept off it during the summer months. This, of course, is a counsel of perfection in the great majority of cases, and 'attempts must be made to keep off the fly and prevent her depositing her eggs by smearing the nostrils and nose with Stockholm tar. This entails considerable labour in the case of large flocks. To avoid it the sheep may be made to dress their own noses by placing salt boxes about, Avith holes cut in the lid or sides, and painted over with tar. Sometimes Vshaped troughs are used, with the sides painted Avith tar, but I think that the closed box or trough is the more practical. Remove Infested Sheep Sheep that become infested should be removed from the flock and kept under observation, so that the maggots may be destroyed as they are ejected.- Remedial treatment may also be tried if it is considered Avorth Avhile. Where there are only a feAv cases to deal Avith, steaming the nostrils to loosen up the discharge and promote its Aoav gives considerable relief Avhen the breathing is embarrassed. Snuff may also be bloAvn up the nostrils to encourage violent sneezing. A feAv ounces of a solution made by dissolving a teaspoonful of common salt in a pint of Avater, and adding a teaspoonful of tincture of iodine, may be injected up each nostril, to free the nasal chambers of mucus and favour the expulsion of the maggots. Fumigations with sulphur, or the fumes of Stockholm tar, may also be tried, but on the Avhole it is better to go to considerable pains to try and prevent the trouble.