Clover Mites Might Become
an Indoor Pest / from

These outdoor arachnids are on the lookout for the perfect harborage.

By Heather Gooch, Managing Editor

Clover mites (Bryobia praetiosa Koch) really prefer your customer's lawn to their basement, but that doesn't keep them from occasionally invading structures. So says Dr. David Shetlar, associate professor of landscape entomology at The Ohio State University, Columbus, Ohio.

"I had a couple of homeowners call in a panic, telling me that clover mites were literally covering the walls in their basement," he recalls. "I asked whether they could me send me some, and a couple days later, a couple strips of masking tape arrived in the mail. This person literally pressed the masking tape lightly to his wall, and it was completely covered with clover mites."

These arthropods typically feed on turf grass, extracting chlorophyll out of the cells of turf grass plants. Whenever it's time to shed their skin or lay eggs, which they do on a regular basis, Shetlar tells Pest Control that clover mites always look for a secluded spot.

"They'll climb up trees and get in the little cracks and crevices of bark, to hunker down and do their business. However, when we grow turfgrass up next to the building, the building turns into a 'tree,' " he explains. "Obviously, if that's the only structural element near the turf, then they can come in by the thousands."

Shetlar recommends that pest management professionals (PMPs) request their customers to not keep any plant material right next to the house, including trees and shrubs. There needs to be enough space between the plant and the house that an adult could easily walk through, he adds.

Dine-o-Mite
"Clover" is a misnomer for this arachnid, Shetlar notes, apparently stemming from finding the mites on clover about 100 years ago. Although they will feed on other plant materials, the favorite snack of clover mites is just about all types of turfgrass. In fact, Shetlar has a telltale sign for PMPs to know whether they're in for a clover mite infestation as soon as they pull up to the account.

"If you really have a sharp eye, the turf looks silvery or frosted on top," he states, explaining that the mites sap the grass blades from the top down. "This is especially prominent right after the snow cover has disappeared. I think a lot of people think it's just winter desiccation, but once you've seen it, it's pretty easy to spot. Of course, later in the spring, after people have mowed the lawn a couple times, that silver topping has been mowed off."

The body of a clover mite is a dark olive green, from the sap they've extracted from feeding on the plant cells. They have eight salmon-colored legs, and typically, when crushed, the mite leaves a light pink stain with a darker green stain next to it.

"That's how a lot of people notice them, the mites will get on the curtains or furniture, someone will sit down on them, get up and if they have light-colored clothing, they find spots on their clothes," Shetlar notes. "It's just like a grass stain-not that easy to get rid of."

Although mites are solitary creatures, they often cluster together in large numbers. They lay round eggs that resemble paprika on just about any kind of vertical structure, such as tree bark or under switch boxes. They need moisture, which is one reason why they often head for a structure's basement.

Shetlar tells Pest Control that clover mites are an unusual pest in that they are a "cool season" mite, which means that they do best in an environment with temperatures of about 35 to 70 degrees Fahrenheit. The mites are most active in the fall, and actually spend the summer in the egg stage. The eggs hatch around late September.

The mites will complete one or two generations in the fall, and then when temperatures drop down to regularly freezing, they'll lay overwintering eggs, which hatch around March.
The eggs technically hatch into a larva, which looks like a tiny mite, but it only has three pairs of legs, Shetlar notes. When it molts into the first nymphal stage, it gains its final fourth pair of legs that make it a true arachnid. Then there's one more nymphal stage, and finally, the adult stage. Adults are about half a millimeter, a little larger than a pinhead.

For PMPs, the mites fall into the category of occasional invaders, a group that includes lady beetles, earwigs and other outdoor pests that accidentally get indoors. For this group, Shetlar says it's important to keep in mind that exclusion is the best method of control.

"No matter what, these pests all need the same basic requirements-food, water and harborage," he states. "So what PMPs need to find out is, what is it at the account that creates this environment?" PC

Managing Editor Heather Gooch is Pest Control magazine's Web master, as well as a regional vice president of the American Society of Business Press Editors (ASBPE) Cleveland, Ohio, chapter.

Copyright © 2001 [Alan Luke]. All rights reserved.
Revised: 06/25/10. Home