Warbles in cats are lumps under the skin caused by botfly larvae burrowing into the body and growing there. The larvae belong to the Cuterebra genus, a group of 34 species found throughout the Americas that normally parasitize rabbits and rodents. Cats pick them up accidentally, usually while exploring burrows or brushy areas during summer and early autumn.
How Cats Get Warbles
Adult Cuterebra flies don’t land on cats or bite them. Instead, the flies lay eggs near the entrances of rabbit and rodent burrows. When a cat sniffs around one of these areas, body heat causes the eggs to hatch, and the tiny, moist larvae stick to the cat’s fur. From there, the larvae enter the body through a natural opening: the nose, mouth, or eyes.
Once inside, the larva migrates through tissue until it settles into a spot just under the skin, typically around the head, neck, or trunk. There it creates a small breathing hole (called a pore) in the skin’s surface and continues to grow, feeding on the cat’s tissue fluids. Cats are not the intended host for these parasites. They most commonly pick up species that normally target rabbits and other lagomorphs, which is why the infestation is sometimes called an accidental or aberrant parasitism.
What a Warble Looks and Feels Like
The first sign many cat owners notice is a patch of matted fur that the cat keeps licking or chewing at. Beneath that spot, you’ll find a soft, well-defined lump about 1 centimeter across with a tiny hole in the center. That hole is the larva’s breathing pore, and you may see a small, dark shape moving inside it.
The swelling can ooze pus-like fluid and may look a lot like an abscess or infected wound, which is why warbles often get mistaken for bite wounds or cysts. The key difference is that visible breathing pore. If you look closely at the lump and see a small opening, sometimes with a bit of the larva visible, that’s a strong indicator of Cuterebra rather than a simple abscess. Cases appear almost exclusively in late summer and autumn, when the larvae are large enough to produce a noticeable lump.
Why You Should Not Remove It Yourself
It’s tempting to squeeze the lump and try to pull the larva out, but this is genuinely dangerous. If the larva ruptures during removal, its body contents can trigger a severe allergic reaction, potentially including anaphylaxis. Fragmented larvae left behind can also cause intense local inflammation and secondary bacterial infection.
A veterinarian will enlarge the breathing pore carefully and extract the larva in one piece, intact, using specialized instruments. This is a relatively quick procedure, often done under light sedation. Once the larva is out, the vet flushes the cavity to clean out debris and typically prescribes antibiotics to prevent or treat any secondary infection. The wound is usually left open to drain and heal from the inside out. Most cats recover fully, and the site closes on its own within a couple of weeks.
Rare but Serious Complications
In most cases, a warble is a localized skin problem that resolves cleanly after the larva is removed. Occasionally, though, a larva takes an abnormal migration path and ends up somewhere far more dangerous than the skin.
Cuterebra larvae can migrate into the brain or spinal cord, causing neurological symptoms. Because the larvae enter through the nose or mouth, they have relatively direct access to the central nervous system. Signs of neurological involvement include sudden changes in behavior, circling, seizures, blindness, loss of coordination, or difficulty walking. These symptoms tend to appear in outdoor cats during the summer months and are often overlooked as a possible cause. Neurological cuterebriasis is a serious condition, and the prognosis depends heavily on how much damage the larva has caused before treatment begins.
Larvae have also been found in and around the eyes. In reported cases, cats presented with fevers that likely resulted from secondary bacterial infection or a hypersensitivity reaction to the parasite.
Which Cats Are at Risk
Warbles are almost exclusively a problem for cats with outdoor access, particularly those that hunt or explore areas where rabbits and rodents live. Kittens and young cats seem to turn up with warbles more frequently, likely because they’re more curious and more likely to stick their faces into burrows and brush piles.
The risk is seasonal. Cuterebra flies are active in summer, and the larvae grow large enough to be noticed in late summer through early autumn. Geographically, all 34 Cuterebra species are found in the Americas, so cats in North, Central, and South America are the ones at risk. Indoor-only cats have essentially zero chance of picking up a warble.
Reducing Your Cat’s Risk
The most effective prevention is keeping your cat indoors during peak botfly season, roughly July through September in most of North America. If your cat does go outside, limiting access to overgrown areas, woodpiles, and known rabbit habitats reduces exposure. There is no vaccine or standard preventive medication specifically for Cuterebra, so environmental avoidance is the primary strategy. Regularly checking your outdoor cat’s skin during late summer, especially around the head, neck, and shoulders, helps catch a warble early before the larva grows large or migrates somewhere problematic.