Dear Dr. Schelling,

My husband takes our dog Buddy hiking with him in the forest, and last week I noticed Buddy was scratching and licking an oozing sore on his side. On closer inspection I found a perfectly round hole under his wet fur and at first thought it was a bullet hole or a bite wound. I cleaned the area as best I could with some soap and water but it has not healed. When I checked it again today I swear I could see a little white caterpillar inside the hole!

I have made an appointment with the vet but I am worried sick about him and concerned that maybe my husband or I will catch something from him.

-Caterpillar in my dog

Dear Caterpillar in my dog,

You don’t know how close to right you are with your diagnosis of Buddy’s wound. More than likely Buddy has been infested with the larvae of a Cuterebra or bot fly. These flies lay their eggs around rabbit or rodent burrows where unsuspecting dogs and cats can encounter them. When the pet grooms, they can ingest or inhale the eggs which go on to hatch into larvae or young worms. These larvae move to the space under the skin, create a large cyst called a warble, and eventually burrow out creating a breathing hole. This is likely when Buddy started scratching it and when you saw what you thought was a caterpillar coming out for air.

Taking Buddy to the veterinarian is the right thing to do. It is important that you not try to treat this condition at home as grabbing the larvae or squeezing the cyst can lead to severe allergic reactions and even anaphylaxis.

Click here to read the article Cuterebra Infestation in Dogs to learn more about Cuterebra flies and how to protect your pets from being infested.

-Dr. Schelling