GRUB IN THE HEAD.
—This condition is the presence of the larva (worm stage) of the sheep bot fly, located in the frontal sinuses (cavities) of the head. The trouble is confined to sheep and occasionally goats. The so-called “grub” of the horse is found in its stomach, while the “grub” of cattle is found along its back just underneath the skin. The adult fly, which lays the living “sheep grub,” is of a yellowish-gray color, slightly larger than a house fly. During the warmer part of the summer days the fly goes about depositing its young in the nose of the sheep. The young then work their way upward into cavities of the head between the eyes, but not into the brain cavity. Here they attach themselves to the lining, remaining when unmolested for some ten months, then lose their hold and are sneezed out to the ground. Burrowing into the ground they enter the pupa or dormant stage, when, after a month or six weeks, they emerge as adult flies to replenish their kind.
When few grubs are in the head little trouble may be observed, but if more numerous may cause free discharge of dirty white or yellowish, thick fluid, loss of appetite, frequent coughing and sneezing, tossing of head and weakened gait, and the animal may become too weak to rise, and finally dies. With a special instrument (trephine) bore a hole into the cavity containing grubs and remove them with forceps. When they are present every year the sheep should be protected by keeping the nose smeared with tar during summer months. This can be done by causing sheep to lick salt from holes in a trough after placing tar about the holes.