The mopane worm, which is the caterpillar form of the Saturnid moth Imbrasia belina Westwood, is like other edible insects and caterpillars a vital source of protein in southern African countries. The worms live and graze on mopane trees, which have alternative uses. With increasing commercialization of the worm, its management, which was hitherto organized as a common property resource, has been degraded to almost open access. This paper uses a bioeconomic modelling approach to show that for some optimal allocation of the mopane forest stock, the restrictive harvest period policy advocated by community leaders may not lead to sustainable harvesting of the worm. © 2009 Cambridge University Press 2009.