No you are not imagining this. The specks are actually moving. That is because they are actually tiny mites called clover mites. Clover mites can become annoying household pests, especially in and around homes where new lawns have recently been established or where there’s a heavy growth of well-fertilized grass close to foundation walls. They enter a home from outside and often become most active near sunny areas – why you see them on windowsills.
These tiny mites feed on grasses, clovers and certain other plants in the lawn and around the home. They often crawl into cracks and crevices to molt and lay eggs. Typical “hiding places” are under the loose bark of trees, on foundations walls, beneath siding and around window frames.
Under magnification, however, they are reddish in color and have characteristically long front legs.
Clover mites are most abundant in the fall and spring and are relatively inactive during the hot summer months and again during cold weather. They migrate into homes either when population pressure becomes too great or when feeding conditions become unfavorable, such as the onset of hot or cold weather.
Clover mites are very tiny as can be seen on this ruler.
The mites are very tiny creatures (smaller than a pin head) and may occur in countless numbers. They usually appear first around windows, but later may overrun entire walls of a home. To most people they appear as tiny, moving, black specks. Under magnification, however, they are reddish in color and have characteristically long front legs. This character helps separate them from the hundreds of other different mites.
Clover mites can be prevented from entering a home or building by using perimeter treatments. These may be either physical or chemical. A physical barrier can be established by separating turfgrass (where the mites feed) from the perimeter wall of the building. A strip of clean cultivated soil or stone, free of grasses, that extends 18 – 24 inches out from the foundation is usually sufficient to deter these mites from crossing. Ornamental plants that are not clovers or grasses may be added to increase the attractiveness.
Chemical barrier treatments may be applied to the outside foundation perimeter (three feet high and three feet out). Soaps as well as pyrethroid insecticides have been shown to be effective IF applied during the times that the mites are on the move.
Use of chemicals inside the home is not recommended. Remember that these mites do not directly damage the building nor do they bite people. Most consider them a temporary nuisance pest only and find that vacuuming or wiping them up with a soft sponge or wet cloth is sufficient. Be aware that they can smear and leave a red stain if crushed.
Tim Gibb, Turfgrass Entomologist