There are two main groups of scale insects, both of which spend most of their lives as immobile adults under a coating, sucking the sap from stalks, leaves and stems. Hard scale (for example red citrus scale) has an oyster like coating and is difficult to control. Soft scale (for example pink wax scale and soft brown scale) are usually found on the mid-rib of leaves and stalks of host plants. Most common is white wax scale, seen as large patches of white waxy material along the stems and shoots. The wax covers the insects which feed on the sap.