Biology
Hydrangea scale is a sap-sucking insect that develops on the underside of leaves on Hydrangea and some other plants.
There is one generation a year with young nymphs hatching from eggs in mid-summer and sucking sap from the undersides of leaves. In late summer the nymphs move to the stems where they overwinter before maturing in late spring. Eggs are deposited under a covering of white waxy fibres in early summer.