what do they look like?
They  vary dramatically in appearance, from very small organisms (1–2 mm) that grow beneath wax covers (some shaped like oysters, others like mussel shells), to shiny pearl-like objects (about 5 mm), to animals covered with mealy wax.
Scale insect
 vary dramatically in appearance, from very small organisms (1–2 mm) that grow beneath wax covers (some shaped like oysters, others like mussel shells), to shiny pearl-like objects (about 5 mm), to animals covered with mealy wax.
what is the scale insect? They are small insects of the order Hemiptera, suborder Sternorrhyncha. are they pests? Yes,  crop pests. what are the various stages of their life? They develop from the egg through a first instar (crawler) stage and a second instar stage before becoming adult.
wiki:20189601
Scale insect [SEP] Description
They are usually slender insects resembling aphids or small flies. They have antennae with nine or ten segments, compound eyes (Margarodidae and Ortheziidae) or simple eyes (most other families), and legs with five segments. Most species have wings, and in some, alternate generations may be winged or wingless. Adult males do not feed, and die within two or three days of emergence.