It always seems to me that creatures that are dependent on a particular plant for their survival are taking something of a risk; if anything happens to their host species then they are doomed! I suppose the dead-nettle leaf beetle (Chrysolina fastuosa) does not have to worry too much as its preferred vegetables are dead-nettles and hemp-nettles which are both widespread and very hardy.
Chrysolina fastuosa is relatively small (between 5mm to 7mm) but stands out in a crowd due to its brilliant metallic green sheen which can also feature blue, red and gold depending on the light and the age of the specimen. Preferring waterside locations they are clearly visible on suitable vegetation where they feed on the leaves. May be this is where they derive their colouration from?
They can be seen from as early as March right through until October and are relatively common.