Pyrrhocoris apterus is a black and red European bug the size of a finger-nail. It is normally found underneath lime trees (Tilia spp.) walking about on the leaf litter and feeding on the fallen seeds. It is readily reared in the laboratory in jars, on a diet of water and dry lime seeds, and with crumpled paper as a substitute for the leaf litter. We have recently found, however, that the nature and source of the paper is important. Reared on the advertisement pages of Nature, growth and reproduction were normal, but on certain other papers all the emergent adults were deformed, superficially resembling the metathetelic (juvenile) extra instars obtained by the implantation of the corpus allatum into last-stage larvae. So far the following samples of paper have been found to produce this effect: pages from Scientific American, paper tissues made by Dixcel and paper tissues and some batches of