Oystershell Scale – Lepidosaphes ulmi

Oystershell scale (lepidosaphes ulmi)

Common Name: oystershell scale

Latin Name: lepidosaphes ulmi


The waxy coating of mature specimens is approximately 2.5 millimeters long, grayish brown, and significantly convex, like microscopic oyster shells. This armored scale forms on the bark of the host plant. Tiny white eggs are discovered behind the female’s waxy coating. Crawlers are the life stages that hatch from eggs. This scale insect’s crawler stage is light yellow and less than one millimeter long. Adult males have just one set of wings. When carefully examined, mature males are misinterpreted as parasitoids as they stroll over infected twigs.

Host plant:

Ash, aspen, cottonwood, lilac, maple, poplar, and willow are all shared hosts for the oystershell scale. Almond, beech, birch, boxwood, apple, apricot, cotoneaster, currant, dogwood, elm, fig, grape, chestnut, linden, plum, quince, raspberry, rose,  mountain ash, pear, peony sycamore, Virginia creeper, walnut, and other plants are also frequent hosts.


It occurs throughout the United States, with northern states being more prevalent than southern states.

Damages caused by oystershell scale:

Infestations often originate on individual host branches. Infested trees’ bark may become scaly and ultimately fracture. The plant will lose its vitality and seem scruffy. The leaves may be discolored and very tiny. Over time, heavy infestations may cause decline and destroy individual branches and even whole trees.

Life history and habits:

The life cycle differs depending on the host tree species. In general, insects overwinter in groups of 50-100 beneath the scale cover in the egg stage. Crawlers emerge in May and search for food on twigs and trees. In July, adult females are present. They have produced a scale covering under which the white eggs are placed by late July.