"This is a juvenile form of the Cereal leaf beetle (Oulema melanopus) after being parasitized by Tetrastichus julis, a parasitoid wasp which lays its eggs inside the larva of the beetle. They eggs hatch within the larvae and begin to feed while it is still alive, before they burst out and kill it.
These parasites are often used as a biological control, as the Cereal leaf beetle is considered a pest and regularly feeds on crops."