Most fifth instar Argina cribraria female larvae reared in paired groups on fresh sunnhemp leaves practised cannibalism on the male. A potential cannibal pounced on the victim and severed its dorsal vessel, causing profuse bleeding of haemolymph, immobility and contraction. The cannibal fed on victim's carcass and might consume 1–2 larvae and 1–3 pupae. More females emerged from an experiment having larval cannibalism. The cannibals were lighter, but the relative titres of sugars, proteins and phenols were higher in cannibals than those in control female caterpillars.