Among the more conspicuous insects we encountered during our Australian travels were Paropsisterna eucalyptus leaf beetles. Most trees I looked at in southern Australia hosted clusters of pudgy yellow larvae hanging around in plain view, munching on the aromatic leaves in happy abandon.
The beetles have good reason to be seen: they are toxic. Unusually among insects, this beetle’s arsenal includes hydrogen cyanide. By advertising this fact to would-be predators, they avoid becoming a bird’s lunch.
source: Moore, B. P. 1967. Hydrogen Cyanide in the Defensive Secretions of Larval Paropsini (Coleoptera: Chrysomelidae). Australian Journal of Entomology 6: 36-38.