Parasitic insects are common causes of skin diseases in domestic animals.
The diseased conditions of the skin, and the irritation that they may cause
the animal, depend on the life history and habits of the parasite. Species
that are unable to live independently of a host and are permanent parasites
are usually the most injurious to the animal. This is especially true of
parasites that are capable of puncturing the skin or burrowing into it.
Temporary parasites may cause fatal forms of disease. This is true of the
larva? of the sheep bot-fly, which develop in the sinuses of the head,
causing severe inflammation of these parts, nervous symptoms and death. The
character of the symptoms of a parasitic disease depends on the habits of
the parasite, and the tissue or organ, that it may attack.