The large Woodrat Bot Fly is a terrible menace to woodland rodents and squirrels as well as domestic cats and dogs, often necessitating a trip to the veterinarian.
Woodrat Bot Flies are members of the the Oestridae family. These large bee mimics do not sting, nor do they bite. This species is, however, a parasite to small mammals in the forest as well as unfortunate pets. The female fly deposits fertilized eggs around the perimeter of a den or hole occupied by a rodent or rabbit. Once the rodent passes by, it picks up an egg in its nose or mouth when sniffing around. The egg, now inside the animal, moves to the outer body, just under the skin. Areas around the throat, stomach, legs, or back are most common landing points. There, the egg enlarges and a tumor-like growth forms on the animal. This growth is called a warble. A small hole is created in the warble (called a warble hole) that allows the hatched fly larva to breathe the outside air. The larva (maggot) is worm-like, plump, and continues to grow in size. When it is ready to pupate, it leaves the warble through the hole and falls to the ground. This usually leaves the animal with a large gaping wound that can easily become infected if not treated. Pets with a warble can be brought to a veterinarian, where the Woodrat Bot Fly larva is removed and the warble hole treated so that it heals. In the wild, a newly-freed larva encases itself on the ground and pupates, emerging as a flying adult.
As a parasite, the Woodrat Bot Fly does not kill its host, but it can make it uncomfortable and even sick if not treated. Unlike ordinary flies, the Woodrat Bot Fly has huge black eyes that may or may not connect to each other. Yellow or golden hairs are easy to see around the mouth and upper legs. If an adult fly is seen in the backyard, it may be prudent to keep on eye on any pets that may have come into contact with eggs. Feeling for bumps that have a wound in the skin can help diagnose and treat an affected animal more quickly.
Scientific Name: Cuterebra americana
Other Name(s): Warble Fly, Heel Fly
Fly or Mosquito
Size (Adult; Length): 20mm to 30mm (0.78in to 1.17in)
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