Harvest Mite Infestations in Dogs

By Malcolm Weir, DVM, MSc, MPH

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 North 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 can be found in berry patches, tall grass, weeds, wooded 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 the animal and attach to the skin, especially on thinly haired areas of skin. The larvae feed for two or three days and then drop off onto the ground to complete the life cycle. The larvae mite is orange and is barely visible to the naked eye.

What do harvest mites do to dogs?

Contrary to popular belief, the harvest mite larvae do not burrow deep into the skin and live underneath it. 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, which become liquefied and are consumed by the larvae. The enzymes are irritating to the skin and result in intense itching. Itching causes the dog to chew or scratch itself, causing self-inflicted wounds. The resulting skin lesions vary from crusted spots to areas of hair loss to raw and moist bleeding areas. In dogs, harvest mites are more commonly found around the ears and between the toes but can be found almost anywhere on the body.

How is 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 dogs 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 microscope 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 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 dog 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.

What can I do to stop the itching?

In most cases, the dog will not require any treatment once the mites are killed. In dogs that are very sensitive to bites from harvest mite larvae, additional treatment with anti-inflammatory medications may be indicated. In dogs 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 ankles 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 and areas known to be inhabited by chiggers.

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