The adult beetles look very attractive with metallic purple and green stripes and measure 6-8mm (around 1/3in) long. They feed on the leaves and flowers for much of the year, with most damage occurring from late summer to spring.
The greyish-white larvae have dark stripes running along their body and measure up to 8mm (around 1/3in) long. They feed on the leaves and flowers from autumn to spring.
In late summer, the adult beetles mate and the females lay their eggs on the plants. When the larvae are fully grown, in spring, they move into the soil to pupate. The adult beetles emerge in early summer. The adult beetles are long lived and can be found on plants nearly all year round.
The first rosemary beetles were recorded in the UK in the 1990s in London, but they have spread rapidly to other parts of the UK since.