Chrysolina americana can reach a length of 5–8 millimetres (0.20–0.31 in). They have colourful elytra with metallic green and purple longitudinal stripes. The wings are quite short, so these beetles can not fly.
In the Mediterranean region females lay their eggs in late summer on the leaves of the host plants. The larvae show whitish to blackish bands. Larval development continues during the winter months. The pupal stage lasts about three weeks. The imago is released in the spring.
Introduction to the United Kingdom
This species was first discovered living outdoors in the United Kingdom in 1994. By 2002 it had become widespread in the London area, and spreading rapidly throughout. Although it is susceptible to some pesticides, it is usually recommended that home growers pick off beetles by hand, or shake them off onto a sheet of paper to remove them, if the plant affected by them is intended for culinary purposes.
Larva on Rosmarinus officinalis