Bot flies (warbles)
categories: Fact Sheet Stinging and Biting Pests
revision date: 2025-12-22 04:24
Photo by: K. Grey/R. Akre
Biology
Bot flies are among the few true insect parasite (a parasite is an organism that lives in another (the host) without killing it). There are two families:
The robust bot flies (Cuterebrids) which include the tropical human bot fly and the rodent bot fly, and the warbles and bots (Oestrids) which include the northern cattle grub, sheep bots, horse bots and several others.
Adult bot flies are typically large robust flies that often resemble bees. The parasitic larvae of bot flies are large, often spiny maggots that live in various tissues of their specific hosts. Sheep bots, for example, live in the nasal sinuses. Cattle grubs meander through the animal and eventually finish development under the skin. When mature, the larvae wriggle out through the skin and drop to the ground where they pupate.
Rodent bot flies have a similar life cycle and are the bots most often encountered in our area. They typically infest their hosts through nasal passages or other moist body openings including wounds. Eggs and larvae are usually found in rodent burrows or other areas commonly used by host animals (typically mice, rats, squirrels, or chipmunks).
Cats and dogs may become infested if they come into contact with newly-hatched larvae. The larvae typically develop under the skin, but in cats they may sometimes be found in the brain or in the trachea (throat), where they can cause difficulty breathing and swallowing. Usually the first symptom noticed is the presence of a lump just beneath the skin with a small breathing hole opening to the skin surface.
Human infestations are possible but very uncommon.
Management Options
Use Integrated Pest Management (IPM) for successful pest management.
Non-chemical Management
Select non-chemical management options as your first choice!
- You may wish to consult a veterinarian if you suspect the presence of bot fly larvae in your pet.
Chemical Management
IMPORTANT: Visit Home and Garden Fact Sheets for more information on using pesticides.
- None recommended
WSU Extension programs and employment are available to all without discrimination.
Evidence of noncompliance may be reported through your local Extension office.
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