The most familiar stage of the oystershell scale is the covering of the full-grown female scale that overwinters attached to the bark. The overall appearance of the scale often is similar to that of the underlying bark and these insects are easily overlooked. Old scales can stay attached to the tree for several years before falling off. The oystershell scale overwinters in Colorado only in the egg stage.
Eggs are underneath the old scale covering of the mother.
At lower elevations, eggs typically hatch in late May or early June. At higher elevations egg hatch may be delayed into mid-June. Eggs from all the scale insects do not hatch at the same time and egg hatch may extend over a couple of weeks. Eggs of oystershell scale with two generations per year are reported to hatch earlier than one generation scales. The crawlers are pale in color, smaller than a pinhead in size.