The magpie moth's "woolly bear" caterpillars are around 35–38 mm when fully grown and predominantly black with lines of red down its sides and back,[1][2] blue spots and tufts of hair on each segment.

By contrast cinnabar caterpillars have smooth bodies with alternating yellow and black rings.

[1] The magpie moth is diurnal which, coupled with its colourful markings means it is often mistaken for a butterfly.

[13] The life cycle of Nyctemera annulata takes 6–7 weeks to complete and requires warm weather with the winter being passed in the pupa stage.

[1][4] The larvae will feed primarily on species from the genus Senecio [2][4] and are able to migrate considerable distances to new food sources when necessary.

[14] When the caterpillar is fully grown it will be approximately 36mm long [1][2] and at this stage it begins to look for a crevice in which to spin its cocoon ready for pupation to take place.

[5] The cocoon becomes black and shiny with yellow markings and the pupa will stay like this for 12 – 35 days.

The complete cycle of Nyctemera annulata takes 6 – 7 weeks depending on the temperature and therefore the time of year.

[1] Due to its bright colour and bitter taste N. annulata is left alone by most bird predators.

[20] Mokarakara is thought to be the name Māori used for N. annulata, their description being that it was a day-flying moth that was black with white spots (Miller, 1952).

Lessiter (1989) recorded that Māori knew butterflies as pūrerehua and that they referred to the pupa as tūngoungou (meaning "to nod").