Clover Mites

Bryobia praetiosa

Clover mites are plant feeders that occasionally invade homes. These mites do not attack people, and although vast numbers of them can enter homes, they will not reproduce under indoor conditions and will perish shortly of their own accord. Since the conclusion of World War II, the mite has become more common as a household pest. This increase in activity may be related in some way to an increased use of lawn fertilizers. The soil nutrient level or plant vigor and the proximity of the lawn to the house are factors that appear to govern the incidence of infestation.

Description

Adult clover mites are one of the larger mites that infest plants. They are 0.75 mm long, reddish or greenish in color, and have a greatly elongated first pair of legs (Fig. 1). Featherlike plates or scales are sparsely arranged on the abdomen. The mites are frequently encountered on windowsills on the sunny side of homes and will move about at a relatively rapid pace.

Figure 1. Adult clover mite.

Life History

The clover mite is a parthenogenetic species that will overwinter in any dry protected location chiefly in the egg stage; however, it can be found in all stages. The overwintering eggs appear in the cracks and crevices of concrete sidewalks, under the bark of trees, and between the walls of buildings, and often can be found in vast numbers within these confines. The clover mite adults will become active as soon as the temperature rises above freezing. The overwintering eggs hatch early in the spring (approximately April 1, or when temperatures are greater than 45°F) and typically will complete only one generation before they aestivate (a type of warm weather hibernation) for the summer. Another generation usually is completed in the fall.

It is during the spring, however, that the mites become the greatest nuisances to homeowners. As early as mid-January, in southeastern Pennsylvania, warm weather spells can produce activity from overwintering mites. Mites located in the vicinity of buildings may climb the exterior walls and gain entrance around windows or doors. If the mites are overwintering under the building siding or within the wall voids, they may become active and enter the living areas rather than exiting to the outside.

Management

Control can be achieved by applying a spray of one of the registered insecticides to the exterior of the house up to the bottom of the first windows, as well as to all shrubs and to the lawn up to 15 feet from the structure. When using a pesticide for this type of control, be sure that the material is labeled for the "site" (shrubbery, lawn, house exteriors, etc.). Misapplication could result in the staining of the home exterior or the burning of plant foliage. Since the eggs tend to hatch after a rain, repeated applications may be necessary. The removal of grass from a 6- to 24-inch-wide band adjacent to the foundation will act as a deterrent to mite invasions. Within the home, the best control method is to use a strong vacuum, which also will prevent the mites from staining surfaces. It is not necessary to chemically treat for mites within the home because they will die there within a few days from dehydration.

Warning

Pesticides are poisonous. Read and follow directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams, or ponds.

Authored by: Steve Jacobs, Sr. Extension Associate

May 2009, Reviewed January 2014