Cuterebra is a North American botfly whose larvae burrow under a cat's skin and produce a characteristic warble — a raised, fur-disrupted lump with a small breathing hole — most often on the neck or shoulders of outdoor cats in late summer and fall. Most cases are simple subcutaneous infestations cured by manual removal under sedation, but a rare migrating larva can cause neurologic disease or upper-airway obstruction that is rapidly fatal if not recognized (Glass et al., 1998, JAVMA). If your outdoor cat develops a sudden lump with a hole, see a vet within a day.
Last reviewed: June 2026
How Cats Get Cuterebra
Cuterebra adult flies lay eggs near rodent and rabbit burrows. Larvae hatch in response to the warmth of a passing host and enter through a body opening — nose, mouth, eye, anus, or a fresh skin wound — or by directly burrowing through thin skin. Cats become accidental hosts when they hunt or investigate burrows. The larva then migrates through subcutaneous tissue and settles in a final location, most commonly the neck, shoulder, or head, where it matures over 30 days, creates a breathing pore, and eventually exits to pupate. The peak incidence in temperate North America is July through October.
What Owners See
The classic finding is a firm, dome-shaped lump 1 to 2 cm in diameter with a central pore the size of a pencil tip. Through that pore you can sometimes see the dark-pigmented posterior of the larva moving. The fur around the lesion is often matted, parted, or licked away. Affected cats are typically not systemically ill — appetite, energy, and behavior are usually normal. A small clear, brown, or bloody discharge from the pore is common. Multiple warbles in the same cat are uncommon but reported.
When Cuterebra Becomes an Emergency
Aberrant migration is rare but life-threatening. As described in Ettinger's Textbook of Veterinary Internal Medicine, larvae that miss their normal subcutaneous destination can migrate through the nasal passages causing severe sneezing and epistaxis, through the upper airway causing acute respiratory distress, through the eye causing ophthalmomyiasis, and most dramatically through the central nervous system causing feline ischemic encephalopathy and sometimes status epilepticus. Acute neurologic signs in a cat in late summer or fall with possible outdoor exposure should raise immediate concern for cerebral cuterebriasis. CNS migration carries a guarded prognosis even with aggressive treatment.
Removal: Do Not Crush at Home
Manual removal at home through a small pore is strongly discouraged. Crushing the larva or rupturing its body releases proteins into surrounding tissue that can trigger severe anaphylactic and inflammatory reactions, sometimes with fatal shock. The correct approach is veterinary removal under sedation: the pore is gently dilated, the intact larva grasped with mosquito forceps, and the warble pocket flushed and debrided. Larvae destroyed in situ rather than extracted intact have caused multiple reported anaphylactic deaths. Ivermectin can be given preoperatively when CNS migration is suspected but is not a substitute for surgical extraction in skin warbles.
After Removal: Healing the Pocket
The empty warble cavity is flushed with sterile saline, debrided, and left open to heal by second intention or partially closed depending on size. Antibiotics are used when secondary bacterial infection is present, which is common. Healing typically takes 2 to 3 weeks. Routine wellness exams and prompt evaluation of new skin lesions in outdoor cats are emphasized as part of broader feline preventive care (AAFP-AAHA Feline Life Stage Guidelines, 2021). The cavity may temporarily look worse than the original lump as inflammation peaks at days 3 to 5. Recheck at 7 to 10 days lets the vet confirm complete extraction — retained larval fragments are the leading cause of treatment failure and chronic draining sinus.
Prevention
Keeping cats indoors during July through October in regions where Cuterebra is endemic — most of North America east of the Rockies and much of California and the Pacific Northwest — is by far the most effective prevention. There is no FDA-approved cat product labeled for Cuterebra prevention. Year-round flea and parasite prevention does not reliably prevent botfly larval infestation, and the timing of larval migration after entry is too fast for typical monthly parasiticides to interrupt reliably. Outdoor cats should be checked weekly during peak months for any new lump or matted fur patch.
When to See a Vet
Call your vet today if:
- A new raised lump with a small central hole on an outdoor cat
- A patch of matted fur with a hidden pore underneath
- Persistent licking, scratching, or biting at one specific area of the body
- A draining sinus that does not close after 2 to 3 days
- Multiple new lumps in a cat with recent outdoor access
Go to the ER immediately if:
- Sudden seizures, circling, blindness, or unilateral weakness in a cat with outdoor access (possible CNS migration)
- Acute facial swelling and difficulty breathing after a cat has been licking at a lump
- Sudden severe sneezing, nasal bleeding, or respiratory distress in late summer or fall
- Sudden ocular pain, cloudiness, or visible movement inside the eye
- Collapse, weakness, or pale gums after any attempted home removal of a warble
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Frequently Asked Questions
Can I pull the larva out at home with tweezers?
Strongly recommended against. The larva's body wall ruptures easily and releases proteins that can cause fatal anaphylaxis. Even if removal looks successful, retained mouthparts or anchoring hooks remain in the pocket and reliably trigger chronic infection. Veterinary removal under sedation costs roughly the price of a single uncomplicated office call and reliably gets the entire larva out intact.
How much does Cuterebra removal cost?
Initial vet exam typically runs $50 to $150 in the US. Sedated removal with debridement and flush adds $150 to $400 depending on lesion location and number. Antibiotics for secondary infection run $20 to $80. Recheck visits are typically $40 to $90. If CNS migration is suspected, MRI is $1,500 to $3,000 and hospitalization can reach $2,500 to $5,000+. Catching it as a simple skin warble is dramatically cheaper than treating a CNS migration.
Is Cuterebra contagious to dogs, other cats, or humans?
No. Cuterebra cannot be transmitted from one infected animal to another. Each infestation requires direct contact with the egg-bearing environment, almost always near rodent or rabbit burrows outdoors. A cat with a warble cannot infect housemates. Humans are very rarely accidentally infested, almost always after direct prolonged outdoor exposure rather than contact with a pet.
Will the lump go away on its own if left alone?
The mature larva will eventually exit and the pocket will close, but the process can take 30 days and carries risk of secondary infection, sepsis, and rarely larval migration to atypical sites. Owners who wait sometimes find the larva exits at night and leaves a chronic draining wound that takes weeks to heal. Prompt removal is faster, safer, and far less expensive than waiting.
My indoor-only cat has a lump like this — could it still be Cuterebra?
Possible but unusual. Strictly indoor cats with no access to porches, garages, or open windows essentially never get Cuterebra. A lump on an indoor cat is more likely to be an abscess, cyst, mast cell tumor, lipoma, fibrosarcoma, or other dermatologic process. Any new lump on a cat deserves veterinary evaluation regardless of indoor or outdoor status.
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