Cuterebra: Botflies and Warbles

Warning: Cuterebra are one of the Grossest things a pet owner or veterinarian might see! You have been warned!

This is a botfly.  These flies are similar in appearance to other flies, but they live an extra gross life.  While most flies lay eggs in compost, manure, or other similar decaying material, botflies lay their eggs in rodent burrows.  The eggs hatch, and the larvae (one larva, two larvae) then attach to the rodents (or a curious dog or cat!).  The larvae make their way into the nose or mouth of the animal and...well, it gets gross(...er). 

The larvae move from inside the body to a place just under the skin, where they start to grow.  This causes a red, often fur-less bump to form, called a warble.  Inside this warble is the growing botfly larva, called a cuterebra.  A small opening at the top of the warble allows the larva to breathe.  Once the larva has grown as much as it can (it can take a month or so), it falls out of the warble onto the ground.  The larva then eventually pupates and turns into an adult botfly, and the cycle starts all over!

Cuterebra are most commonly seen in outdoor animals, such as cats, rabbits, or hunting dogs.  If you think you might see a warble on your animal, be sure to talk to your vet right away!