These annoyances are another result of turning an animal out to grass, the fly whence the trouble is derived never entering the stable. The insect rejoices in the freedom of the field; and man, by turning out his horse, finds the creature a fitting spot for the deposit of its eggs. This body is carefully deposited upon the back or sides. The warmth of the animal hatches the larva; no sooner is it endowed with life, than, with the instinct of its kind, it burrows into the skin. The integument of the horse, however thick it may appear, is soon pierced by the active little maggot, which, thus snugly housed, retains its lodging until the following spring. During the winter, a small lump denotes its abiding place; but as the second summer progresses, a tolerably large abscess is instituted.
a. The winter residence of the larva.
b. The summer abode of the insect.
c. A drop of tallow falling upon the center of the abscess.
DIAGRAM OF THE LARVA ABSCESS, DIVIDED THROUGH ITS CENTER.
1. The spot through which the larva breathes.
2. The insect, full size.
3. The mouth of the parasite.
4. The pus surrounding the body, and upon which the creature lives.
5. The sac of the abscess.
6. The fat of the horse, or the adipose tissue much swollen and inflamed.
7. The skin.
8. The superficial muscle.
9. The muscle proper to the body of the animal.
The interior of the abscess, of course, contains pus. Upon that secretion the insect lives and thrives. The inhabitant of a warm abode, and surrounded by its food, the early period of life no doubt is, for an inactive being, highly agreeable. A division of one of these abscesses, when fully matured, is represented in the second cut, page 233.
Such swellings are acutely painful and prove the sources of much annoyance. They mostly occur upon the back. The saddle cannot be laid on one of these tumors; and, as the spine supports much of the harness, the proprietor has the vexation of beholding his horse rendered perfectly useless; for suffering, should service be exacted, occasions the creature to excite displeasure; besides, the pranks thus provoked by torture often continue after the cause has been removed.
Upon the summit of the abscess appears a black spot. It is at this spot the larva receives the air needed to support a dormant existence. This fact being known to certain people, the knowledge is employed to destroy the parasite. The swelling is first slightly greased, and then a drop of melted tallow is let fall upon the breathing place. By such means the insect is effectually suffocated, and assuredly dies.
Others employ a darning needle as the instrument of execution. The needle is thrust through the central spot into the swelling for three-eighths of an inch. The larva thereby is pierced, and the life certainly is sacrificed.