Chrysolina cerealis, the rainbow leaf beetle or Snowdon beetle, is a brightly coloured Eurasian leaf beetle. It is found in montane grassland from Norway to northern Italy, and from Ussuri in the east to Snowdonia (Wales) in the west. It lives on base-rich screes and lays its eggs on grasses such as Agrostis capillaris and Festuca ovina, although it mostly feeds on the wild thyme Thymus polytrichus, preferring the flowers to the leaves. The beetle is 5.5–10 millimetres (0.22–0.39 in) long. with elytra striped red, gold, green and blue. Females are typically larger than males.
Within Wales, C. cerealis is found at only a few sites on the western flanks of Snowdon, and perhaps in Cwm Idwal in the neighbouring Glyderau. The population is thought to be genetically distinct, and the species is classified as endangered in the UK and protected under Schedule 5 of the Wildlife and Countryside Act, 1981. The species has not been found since 1980 in Cwm Idwal, and some reports consider the Snowdon population of about 1000 adults to be in "serious decline", while others say that there is no evidence of a decline, but that the species may always have been rare.
- Lech Borowiec. "Chrysolina cerealis (Linnaeus, 1767)".
- Ben McCarthy & Kate Van Den Ende (2006). "Snowdon Beetle (Chrysolina cerealis)". Snowdonia National Park Authority.
- "Chrysolina cerealis". ARKive.
- "Rainbow leaf beetle (Chrysolina cerealis)". UK Biodiversity Group Tranche 2 Action Plans – Volume IV: Invertebrates. 1999.