There are four distinct stages in the life cycle of Stethorus and it is important to recognise each of these stages. The elongated, translucent to pale brown eggs are laid singly under the leaves, either on or close to the mite colonies. The eggs are about 0.2 mm long and can easily be distinguished from the smaller spherical (and usually more numerous) mite eggs. Mite eggs are not visible to the naked eye, and a hand lens would be necessary to view them in the field.

Larvae are hairy and vary in colour depending on their age. Larvae go through four stages of maturation, each separated by a moult. Young larvae are pale cream becoming dark grey at maturity. Fourth-stage larvae eventually stop feeding when they are about 2 mm long and attach themselves to the leaf where they pupate.

The pupae are black, hairy and about 1 mm long. Pupae may be found anywhere on the underside of the leaf; however, they tend mostly to be found close to or on the midrib. The pupal stage is easily seen on a leaf, as a skin remains after the adult emerges. To determine whether a pupa is alive or is simply an empty pupal skin, smear it gently with a finger. A wet streak will indicate it was alive and if no wet streak is produced it, was an empty skin.

Adults are shiny black, almost circular beetle and are about 1 mm long. They also occur on the underside of the leaf. Where there is a high incidence of mite infestation, there may be more than fifty adults under one leaf, although there are usually less than ten when mite populations are in check.