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Revised August 2000

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Contents

• Life history
• Physical control
• Chemical control
• Use pesticides wisely and safely

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Clover Mites

Richard M. Houseman
Department of Entomology

The clover mite, Bryobia praetiosa Koch, is a tiny relative of spiders and ticks. Thousands of them can appear during spring or fall, and they are often found crawling around windows or other areas of the home. Clover mites are distinguished from other species of household-invading mites by their reddish-green color and characteristically long front legs (Figure 1). The front legs are as long as the body and almost twice the length of the other legs. These distinguishing features can be seen with the aid of a magnifying glass.

Clover mites can invade a house in extremely large numbers through cracks and tiny openings around windows and doors. One author noted the presence of approximately 250,000 clover mites on the floor of a single bedroom. A heavy growth of well-fertilized grass growing against the foundation of a home is often the source of an infestation. Clover mites do not bite people or pets and cannot cause damage to human structures but they can leave unsightly stains on light-colored walls, carpet, fabrics, or papers when crushed.

Clover mites are plant feeders, and obtain nutrients by sucking plant juices. They usually prefer clovers and lawn grasses but will also feed on certain ornamental shrubs and trees. The abundance of soil nutrients appears to be linked to clover mite populations. Greater populations of clover mites are often associated with newly established lawns or old lawns that have been heavily fertilized.

Figure 1
Clover mite.

Life history

Female clover mites lay bright red eggs in protected areas such as cracks and crevices where they stay relatively dry. Females can produce viable eggs without fertilization (parthenogenesis); males are unknown. The eggs hatch during spring and fall when temperatures are between 70 and 85 degrees Fahrenheit. The resulting offspring are genetically identical to the mother. After hatching, immature clover mites begin to feed on plant juices. There are four stages of development-larva, protonymph, deutonymph, and adult. Only the adults lay eggs. There are usually five or six generations per year.

Clover mites are generally active during spring and fall, when temperatures are favorable. They are usually inactive during summer and winter. In the spring, feeding and egg laying increases until summer temperatures reach 85 degrees Fahrenheit. Adults and eggs remain dormant during summer when temperatures rise above 85 degrees Fahrenheit. When cooler temperatures return in the fall, the eggs will hatch and feeding and egg laying activities continue until winter. Adult mites and eggs overwinter in protected areas. Clover mites generally remain inactive throughout the winter but can become active during brief periods of warm weather during late winter and early spring.

Physical control

Prevention is the most important step in controlling populations of clover mites. Creating a zone free of grass and weeds around the foundation of the home is very important. Clear a strip about 18 to 24 inches wide, especially on the south, southwest, and east sides of the building. These areas can be covered with flowerbeds, pea gravel (mites have difficulty in crawling across it), or left barren. Flowerbeds planted with zinnia, marigold, salvia, rose, chrysanthemum and petunia, or shrubs such as barberry, juniper, spruce, arborvitae, and yew make better barriers because these plants are not attractive to clover mites.

Exterior cracks around doors and windows or holes in the foundation should be caulked. In many instances, this will deter the migration of clover mites into the structure. If mites are still successful at entering the house, vacuuming will collect many of the mites around windowsills, walls and elsewhere without crushing them. Be sure to seal the vacuum bag before disposal.

Chemical control

Under conditions of heavy infestation, the use of insecticide or miticide spray will provide control when properly applied and maintained. However, chemical treatments provide only temporary relief if no physical control measures are practiced.

Outside
Spray the foundation, exterior walls (up to the bottom of the first floor windows) and a strip 10 to 20 feet wide from the foundation out into the grass.

Spray the foundation and walls to the point of runoff. Spray the vegetation until it is thoroughly wet, which usually requires 2 to 4 gallons per 1,000 square feet, depending upon the height and density of the vegetation. Repeat applications as needed. Use any of the pesticides listed in Table 1.

Inside
To control clover mites that have entered the home, use a spray containing synergized pyrethrins. Direct contact is necessary. Repeated application might be required because these materials give no residual control.

Table 1
Pesticides for outdoor use.

Use pesticides wisely and safely

• Apply only where needed or justified.
• Use care when handling, mixing or applying pesticides.
• Keep pesticides in original containers complete with labels.
• Keep pesticides out of reach of children.
• READ, UNDERSTAND and FOLLOW directions on the label and heed all precautions.
• Carefully and properly dispose of unused portions of diluted sprays and empty pesticide containers.
• Do not contaminate food or dishes.

G7358, revised August 2000