Botfly Infestation: How to Handle Warbles in Cats

Jennifer Coates, DVM
By Jennifer Coates, DVM on Sep. 20, 2016

By Jennifer Coates, DVM

You’re petting your cat and you feel a lump. What do you do? Take a closer look of course. You carefully part the fur and now you can see a little hole in the skin too, but wait, it looks like something’s in there … and it’s moving! After you get over your disgust, you’re bound to wonder what could possibly be wrong with your cat. Chances are, you’re dealing with a botfly. Let’s take a look at what botflies are and how they affect cats.

What is a Botfly?

Botflies (also known as Cuterebra) are found all over most parts of North America, although the northeastern United States is a botfly hotspot. Adult botflies (large, fuzzy flies that look a little like bees) lay their eggs near the entrances to their host animal’s burrows (rabbits, rodents, etc.). These eggs hatch and larvae emerge when a potential host is nearby. The larvae grab on to the animal’s fur and then enter the body through any opening (like the nose, mouth or anus). Once inside, they migrate through the body until they arrive in the tissues under the skin. Once there, they make a small hole so they can breathe, continue maturing and eventually emerge and fall to the ground where they become pupae and then adult flies.

How Do Cats Get Botflies?

Most species of botfly have developed a parasitic relationship with one type of mammal, but occasionally they get confused. That appears to be what happens with cats. Since cats love to hunt small mammals, they are attracted to their burrows. While they are poking around there, a botfly larva may mistake them for a rabbit, for example, and hop aboard. Once on a cat, the botflies proceed through their lifecycle as if they were infesting their host species even though it appears that the adult flies that result are not able to reproduce due to this mistake.

Symptoms of a Botfly Infestation

Feline botfly infestations are quite common. All ages and sexes of cats can be affected as long as the individual has access to the outdoors. In northern regions, most cases are seen in the late summer and early fall since botflies cannot be active in the winter. Cases can occur year-round in parts of the country that do not experience cold winters.

The most common symptoms of a botfly infestation is the presence of a lump under the skin accompanied by a small hole through which a thin, relatively clear liquid drains. Cats may lick or scratch at the area causing hair loss and irritating the surrounding skin. Occasionally, migrating larva can end up in unusual locations within the body including the eye, nostrils, throat, chest and brain. Symptoms will depend on what part of the body is affected. For example, the neurologic disease feline ischemic encephalopathy is caused by Cuterebra larvae migrating through the brain.

How to Treat Warbles in Cats

The lump under the skin of a cat infested with a botfly larva is called a warble. In order to get rid of it, you’ll need to make an appointment with your veterinarian. He or she can remove the botfly larva and recommend any follow up care that might be needed to ensure that your cat heals uneventfully. Veterinarians can remove warbles in a number of different ways, including:

  1. Anesthetizing the cat, surgically widening the opening in the skin and removing the botfly with a pair of hemostats or tweezers.
  2. If the opening in the skin is large, the botfly is small and the cat is cooperative, surgery may not be necessary. The veterinarian may sedate the larva with an anesthetic and then pull it out.
  3. Alternatively, some doctors will place a liquid or salve into the hole that eliminates the larva’s ability to breathe. The botfly will usually soon start to emerge at which point it can be grasped and pulled out.

The most important part of treating warbles in cats is to make sure that the entire botfly larva is remove without significant damage to its body. Crushing it or leaving a piece behind can lead to chronic infections or a potentially fatal allergic reaction called anaphylaxis.

How to Prevent Warbles in Cats

The easiest way to prevent warbles is to stop your cat from going outside. If this is not feasible, it is possible that treating your cat monthly with a parasiticide like ivermectin (Heartgard), fipronil (Frontline), imidacloprid (Advantage), or selamectin (Revolution) might prevent warbles in cats even though definitive research has not yet been done.

pasSsy via Shutterstock 

Jennifer Coates, DVM


Jennifer Coates, DVM


Dr. Jennifer Coates is an accomplished veterinarian, writer, editor, and consultant with years of experience in the fields of veterinary...

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