A warble wormhole is the hole created in a host animal's skin by the maggot form of a botfly, a fly of the genus Cuterebra. Once the worm is removed from the cat, it takes anywhere from two to four weeks for the hole to heal.
Cats that go outdoors risk coming into contact with the eggs of botflies, mostly during the summer months. These large flies don't bite, but their eggs sometimes get into a cat's coat from blades of grass or other vegetation that the cat brushes against. When the larvae hatch, they travel into the cat's system either through an orifice or a wound and end up just under the cat's skin. From there they create a pouch of sorts with a hole in the skin for breathing.
When the worm is spotted, the worm has typically been in place for about a month. The instinct is to remove it on the spot. Resist this urge because the worm needs to be removed whole, or the cat is at risk for a nasty immune response, according to PetMD. This is work best done by a veterinarian. The good news is that once it's done, the cat heals fairly quickly and experiences little ill effect.