Harvest Mite Infestations in Cats

What is a harvest mite? 

Harvest mites, also known as red bugs, trombiculid mites, scrub-itch mites, berry bugs or, in their larval stage as chiggers, are mites that are commonly found in forests and grasslands. Harvest mites are relatives of spiders. They are nearly microscopic measuring only 1/100 of an inch (0.4 mm) and have an orange hue. A common species of Harvest mite in Northern America is Trombicula alfreddugesi. In their larval stage, they attach to various animals including humans, cats and dogs. Harvest mites most frequently infect humans and animals in the fall, hence the name "harvest" mites.

"The six-legged larval stage is the only stage that feeds
on warm blooded animals."

The six-legged larval stage is the only stage that feeds on warm blooded animals, especially rodents. All other stages of the Harvest mite live in the environment and are not parasitic. Harvest mites often live in berry patches, tall grass and weeds, woody areas, pine straw, leaves, and bark or mulch. The adult harvest mite, which has eight legs, feeds on vegetation. The larvae are active during the day, especially in dry, sunny weather. When a warm-blooded animal comes into contact with the larvae, they swarm onto it and attach onto skin, especially in thinly haired areas of skin. The larvae feed for two to three days and then drop off onto the ground to complete the life cycle. The larval mite is orange and barely visible to the naked eye.

What do harvest mites do to cats?

Contrary to popular belief, the Harvest mite larvae do not burrow deep into the skin and live underneath the skin. Instead, the larvae live on the skin's surface. During feeding, they pierce the skin with their small, hooked fangs and inject powerful enzymes that digest skin cells, that become liquefied and are consumed by the larvae. The enzymes are irritating to the skin and result in intense itching. Itching causes the cat to chew or scratch itself, causing self-inflicted wounds. The resulting skin lesions vary from crusted spots to areas of hair loss to raw moist bleeding areas.

In cats, Harvest mites are most commonly found around the ears and between the toes, but can be found almost anywhere on the body.

Individual cats vary greatly in their sensitivity to the bite of the mites. Cats that are frequently bitten may develop allergies to the mites resulting in severe clinical signs.

How is a harvest mite infestation diagnosed?

A sudden onset of intense itching during the late summer or early fall suggests that harvest mites or a similar ectoparasite such as fleas may be present. Many cats will ingest the biting larvae while grooming and owners may not see any of the characteristically orange insects.

Your veterinarian will make the diagnosis by identifying the mite. Accumulations of mites may be seen as intensely orange spots on the skin. If fewer mites are present, they may be seen on microscopic examination of a superficial skin scraping.

How do I treat Harvest mites?

Your veterinarian will prescribe safe and effective treatment. There are currently no products licensed for the treatment of harvest mites in cats and dogs. Many insecticides approved for flea control on cats will effectively kill harvest mites, if they are correctly applied. It is important to choose a product with good residual activity and to confine the cat indoors during harvest mite season.

"Applying rubbing alcohol will not kill the chiggers or help with symptoms."

Applying rubbing alcohol will not kill the chiggers or help with symptoms. Alcohol will only cause burning pain and discomfort to the patient.

What can I do to stop the itching?

In most cases, the cat will not require any treatment once the mites are killed. In cats that are very sensitive to bites from harvest mite larvae, additional treatment with anti-inflammatory medications may be indicated. In cases with secondary skin infections, antibiotics may be needed.

Do harvest mites affect people?

People can be affected by harvest mites. Harvest mites are not spread from cats or dogs but from infested outdoor environments. The mites typically attach to people's ankle when they walk through infested vegetation.

"A typical human skin reaction consists of an intensely irritating rash."

A typical human skin reaction consists of an intensely irritating rash. Specific treatment is usually unnecessary and the larvae are removed during bathing. Prevention is best achieved by wearing long pants and socks when walking on trails or woods during the late summer, avoiding high grass or weeds or areas known to be inhabited by chiggers.