Cuterebra (Warble) Infestation

Cuterebra infestation, sometimes called warbles, is caused by the larvae of botflies belonging to the genus Cuterebra. These flies normally parasitise rodents and rabbits, but cats — being enthusiastic hunters that poke around burrows and undergrowth — quite often become accidental hosts, especially in late summer and early autumn when the larvae are active.

The story usually begins outdoors. Adult flies lay eggs near the entrances to rodent and rabbit burrows. When a cat investigates or hunts in these spots, tiny larvae attach and enter the body through the mouth, nose, or a break in the skin. Over the following weeks the larva migrates through the tissues and settles just beneath the skin, where it grows inside a small pocket. It keeps a breathing hole open to the surface, which is often the first thing an owner notices — a firm swelling with a little hole, sometimes with a dark, maggot-like larva just visible inside.

Most warbles form on the head, neck and trunk. While a single, well-placed larva is more unsightly than dangerous, the removal must be done properly. If the larva is crushed or torn during removal, its contents can leak into the tissues and provoke a severe allergic or inflammatory reaction, so this is a job for a vet, not for home squeezing.

Occasionally larvae wander off course and migrate to sensitive places — the eye, the airways, or even the nervous system — where they can cause serious and sometimes dramatic signs such as breathing difficulty, neurological problems or eye damage. These aberrant cases are uncommon but are the reason any unusual lump or sudden illness in an outdoor cat during warble season deserves veterinary attention.

Treatment is straightforward when caught early: the vet removes the intact larva, flushes and cleans the cavity, and prescribes antibiotics if the wound has become infected. Healing is usually rapid. Since there is no preventive drug, the best defence is limiting outdoor roaming and hunting during the peak botfly months.