Legless females hard to recognise

This excellent photograph of native scale insects on leaves of a southern rata tree was taken by Dr Keith Probert, who also extracted some of the dark brown nymphs from their cases.

Scale insects are true bugs belonging to the order Hemiptera, suborder Sternorrhyncha, and comprise the infraorder Coccomorpha.

They are all truly related, forming a monophyletic group.

Female scale insects are highly modified for their way of life. They pass through two or three nymphal or larval stages, before finally moulting into a stage which looks much like a larval stage but develops ovaries and can reproduce sexually.

Females can also reproduce asexually.

Unlike the females, male scale insects are normal-looking insects with a head, thorax and abdomen, long antennae, wings and legs, but the legs have one-segmented tarsi with only a single tarsal claw, whereas all other legged, male true bugs (order Hemiptera) have a double tarsal claw.

The common name "scale insect" comes from the females, which often lose their limbs and become covered with a scale formed of cast-off skins glued together, which renders them difficult to recognise as insects.