Insect identification > Homoptera > Scale insects > Oyster-shell scale

Oyster-shell scale

The oyster-shell scale (Lepidosaphes ulmi L.). - This insect, native to Europe, has been so long in this country that it is now very generally distributed. It is chiefly an enemy of the apple, pear, poplar, willow, ash and lilac but is often found on other plants. It feeds on all parts covered by bark, and the male scales are also often found on the leaves. The full-grown female scale is about one-eighth of an inch long and has much the form of an oyster shell, one end narrowly rounded, the other rather more broadly so, and the shell as a whole usually bent somewhat to one side. It is brown to gray in color, varying with age and, to some extent, the plant it is on. During the winter, examination of the scale will show beneath it, at the narrower end, the dead body of the insect, and behind it from 15 to 100 tiny whitish eggs.

These hatch the following May or June, according to the advancement of the season, into very small whitish nymphs or "crawling young," which are extremely delicate and with no scale. These young crawl out from beneath the parent scale and wander about for a few hours or even a day or so, seeking for places where they may settle; then each thrusts its beak through the bark and begins feeding, and degeneration of eyes, antennae and limbs and the secretion of wax over the body begin. To this secretion the molted skin is added at each molt, making a very tough, hard, covering scale. The insect beneath this becomes adult after a time and following the laying of its eggs, dies.

In the Northern states the eggs are laid in August or September, but in the middle states and farther south, the earlier seasons permit hatching enough earlier in the season for the adult condition to be reached and the eggs laid by midsummer, and these eggs soon hatch and produce egg-laying adults before the following winter. Thus this insect, though having but one generation each year in the more northern states, has two from about the latitude of New Jersey southward, except at such altitudes as to produce northern conditions.

Many of the scales they form of the females. still under their small two-winged undergone a complete metamorphosis. Some entomologists consider the scale on the elm a different species from the one on the apple.