Hostbehaviour manipulation was examined in caterpillars, Pieris brassicae , parasitized by the gregarious braconid wasp, Cotesia glomerata. Following egression of the parasitoids from the host, the moribund caterpillar remains on the pupating parasitoids, spins a web over the parasitoid cocoons, and responds aggressively when disturbed. Cross-species experiments indicated that C. glomerata, but not the congener C. rubecula, has the capacity to interfere with the post-egression behaviour of the host. Dying hosts are viewed as a transient 'functional extension' of the parasitoid that may contribute to parasitoid survival during pupal development by protecting the pupae from natural enemies. This is thought to be the first report on hostbehaviour manipulation that occurs beyond the intimate physical association between the parasite and the host.