Warbles (Fly Larvae) - Environment and Conservation

Warbles (Fly Larvae) Warble Fly

Warbles are the larvae of the warble fly (Hypoderma tarandi) which lays its eggs on
the hair of the caribou’s legs and lower body in mid-summer. Once the eggs hatch, the larvae (maggots) penetrate the skin of the caribou and start a long migration towards the animal’s back.

Hunters may see signs of these migrating larvae in the fall when skinning out an animal. At this early part of the larvae’s life, they are about the size of a small grain of rice and are almost transparent. They may be seen on the surface of the muscles or under the skin.

Through the winter and into the spring they continue their migration up to the spine and rump of the animal where they cut a breathing hole through the skin.

By early summer the warbles are about 1 inch (2.5 cm) long and are ready to emerge from the back. They then fall to the ground and pupate. From the pupae emerges the adult fly that only lives long enough to mate and lay its eggs on another caribou. The adult lives such a short time that it doesn’t even have mouth parts to feed.

The growth and emergence of the larvae and the buzzing of the adults around the caribou as they try to lay their eggs can be very annoying to the animal. At this time of year they may be appear agitated and are sometimes seen jumping around to avoid the irritation.

The infestation usually does no harm to them other than annoyance and is not considered to have any public health significance. The hides of animals that have been affected can often have 100's of holes or scars in them from the emerging larvae and therefore have minimal value for leather.

This infestation is not considered to affect other animals. Cattle often have warble flies of their own but these are of a different species.