Saint John's Wort Beetle

The Saint John's Wort Beetle (Chrysolina hyperici) is a small leaf beetle in the family Chrysomelidae, recognized by its domed, oval body and a metallic sheen that ranges from deep bronze to iridescent green or blue depending on light and population. Adults typically measure between 5 and 8 millimetres in length, with smooth, punctate elytra that give the surface a finely stippled texture under magnification. This species is classified as Critically Endangered (CR) by the IUCN, a status that reflects severe range contraction and localized population collapse in areas where it has historically occurred.

Chrysolina hyperici is closely tied to its namesake host plants, Hypericum species, particularly Hypericum perforatum, feeding on foliage as both larvae and adults in a relationship that makes it highly vulnerable to changes in host plant availability. Historically documented across scattered temperate grassland and open woodland-edge habitats in parts of Europe, its current distribution is now fragmented and considerably reduced, with many former sites showing no recent confirmed records. Population trend data are currently unknown, underscoring a critical gap in monitoring for this species and the broader challenge of tracking small, host-specific insects.

Despite this uncertainty, there are encouraging signs: renewed interest in Hypericum-associated invertebrate surveys across parts of its range has begun generating updated occurrence records, and habitat restoration projects focused on calcareous grasslands may incidentally benefit remaining populations by preserving host plant stands. Continued attention to site-specific surveys and host plant conservation will be essential to clarifying the beetle's true status and preventing further decline of this narrowly specialized species.

This beetle occupies open, sunny habitats such as dry grasslands, meadow margins, and scrubland edges where its obligate host plant, St John's Wort (Hypericum perforatum), grows in sufficient density.