MANY insects contain carotenoid pigments1, and some notable examples are found in the Coleoptera, where carotenoids are responsible for the yellow colour of the yellow and black striped wing cases of the Colorado beetle, Leptinotarsa decemlineata, and the orange-red colour of the ladybird beetles, Coccinella spp. There has, however, been no report of any insect species being able to synthesise carotenoids de novo, and it is generally accepted that in insects, as in other animals, any carotenoids present are of dietary origin2. In July 1976 the Liverpool area, like many regions of the UK, experienced an invasion by enormous numbers of ladybirds, almost entirely of the sevenspot variety, Coccinella septempunctata. With such large numbers of insects available we were able to use modern analytical techniques to identify the carotenoids of these beetles. We report here that the carotenoids identified were mostly hydrocarbons, and the carotenoid pattern indicated that these pigments in the ladybird are likely to be of microbial rather than plant origin, thus suggesting the involvement of symbiotic microorganisms.