Clover mites, Bryobia praetiosa, are more closely related to ticks than they are to insects. They feed on grasses and over 200 different plants in the landscape. When they occur in large numbers, they can cause parts of a lawn to take on a bronze or silvery appearance. These mites will sometimes invade homes and other structures through cracks, under doors, and around windowsills. They are usually more numerous on sun-exposed surfaces.
The size of clover mites is smaller than a pinhead, about 1/30 inch. They are usually rusty red in color but may also appear olive green. If these mites are squashed, they leave a red stain that is difficult to remove from fabrics or walls. If you look closely at these mites, you will notice their long front legs, which are twice as long as their other legs. They hold these front legs out in front of the body, making them look like antennae.
The clover mite is a cool-season mite, developing best at temperatures around 69˚ F. They deposit their eggs in the fall under the bark of trees and in cracks around buildings. In spring, the eggs hatch and the tiny larval stage, having only six legs, appears. They have two more molts as nymphs and will have eight legs from this point on in their life cycle.
The average time required for the clover mite to develop from egg to adult is about one month. This varies with temperature. In spring, the mites may begin entering structures. Following the onset of warmer temperatures, the mites go into a summer hibernation and become inactive until the cooler temperatures of fall. When the clover mites appear in the fall, they may again enter structures. There are no known male clover mites. Females reproduce on their own.
Clover mite control is usually not very difficult. If possible, remove grasses and weeds from around the foundation of the structure, leaving a bare strip about 18 inches wide. This strip can be filled with pea gravel or with plants that are not appealing to clover mites, such as marigold, zinnia, rose, chrysanthemum, petunia, or other flowering plants, or shrubs like spruce and juniper. Entry points that allow mites to come into the structure, like cracks, crevices, doorways, or windowsills, should be caulked or sealed with weather-stripping. If they do come into the house, use a damp cloth to remove them, but do not crush them! Remember, clover mites can stain walls, flooring, and fabrics permanently. Vacuuming is effective for removal, but the vacuum bag should be placed in the outside trash because the mites could escape.
Chemical control should only be necessary with heavy infestations. Using a labeled miticide or insecticide, spray grassy areas around the house where the mites may enter, and trunks of trees and shrubs that may harbor mites. More than one treatment may be necessary for effective control.
Select a control product that will not damage plants. Most products should be safe, but read the label before spraying. Follow all instructions carefully.
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Originally published 06/99