Ear problems in general are uncommon in cats, but among the afflictions that do occur, ear-mite infestation is frequently diagnosed. Although it can’t hop or fly, an ear mite—otherwise known as Otodectes cynotis—can crawl. And if one of these miniscule parasites enters your cat’s ear, makes itself at home, and starts to breed, it can cause major damage unless promptly evicted.

The typical external signs are quite obvious: the cat’s outer ear is likely to be inflamed, and the animal will hold its ears flat against its head, scratch at them almost without letup, and shake its head frequently—as if trying to dislodge a bothersome object. They are also detectable by the mess they make inside an infested animal’s ear canal—a dark, gooey, foul-smelling accumulation of wax and mite debris in which the tiny critter thrives.

“If the newly acquired mite is taking a stroll along a cat’s backside or belly,” says William Miller Jr., VMD, a professor of dermatology at Cornell University’s College of Veterinary Medicine, “the animal will groom it away with its tongue and swallow it. But the parasite is safe if it can make its way to the ear canal, where the cat’s paw or tongue can’t get at it.”

Ear mites are almost microscopically tiny, “about the size of a pinhead,” says Dr. Miller. But, he notes, it’s possible to see their rapidly moving little bodies with the naked eye. Ear mites are extremely contagious, he notes, moving from one cat to another on close contact and eventually making their way to the ear. Infestation is most common among outdoor cats, whether they’re brawling or cuddling up affectionately.

If ear mite infestation is suspected, the cat owner should seek veterinary care without delay. Aside from relieving the animal’s discomfort, treatment can curb infection stemming from the mutilation of the ears and face that results from aggressive and nonstop scratching. Veterinary care can also prevent a serious ear disease called otitis externa—an infection of the outer ear that, if untreated, can progress to the middle and inner ear and damage the ear drum, which can permanently affect the animal’s hearing and sense of balance.

A veterinarian can readily diagnose suspected ear mite infestation by using an otoscope, a flashlight-like instrument used to explore the depths of the ear. If the cat is unwilling to allow this instrument near its sensitive ears, the veterinarian will use a cotton swab to gently collect a sample of ear debris for conclusive microscopic examination.

Treatment generally begins with a thorough cleaning of the cat’s ears to remove any wax or debris that may shield the mites from topical medications. “There are many topical, oral, and systemic agents,” Dr. Miller notes, “and most—such as ivermectin—are highly effective. Even one old-time remedy—baby oil—can do the job. A few drops put into an affected ear several times a day for a month or so will usually smother the mites.”

Subsequent treatment for mites as well as ongoing maintenance of a cat’s ears, says Dr. Miller, can generally be done at home—as long as the owner has been given proper instruction by a veterinarian.