Any of several dipteran species ( botfly family Oestridae or the family Hypodermatidae), widespread in Europe and North America.
The warble flies Hypoderma lineatum and H. bovis , also called cattle grubs or heel flies, are large, heavy, and beelike. They deposit their eggs on the legs of cattle. The larvae penetrate the skin, migrate through the body, and produce a lump, or warble, on the animal's back. Mature grubs emerge and drop to the ground to pupate. Warbles contain breathing holes, which reduce the hide's commercial value. One species ( Oedemagena tarandi ) is a reindeer pest that also causes economic losses.