Soon after amputation of a leg from a final instar larva, granular haemocytes, supported by strands of clotted haemolymph plasma, form a thin cap over the wound, providing the initial wound closure. Cut nerves also appear to attract granular haemocytes and promote organization of a cell sheet covering the wound. Gradually, congregating cells transform the original sheet of cells into a sealing haemocytic plug. Within and across the plug, granular cells form a densely-packed, primary layer like a diaphragm that soon becomes melanized. This is followed later by one or more deeper, secondary layers which also melanize, but to a lesser extent. The primary, melanized layer serves as a pseudocuticle. Its position appears to be determined by the reorganizing epidermis at the wound edge. Presumably the melanized cell layers reduce leakage of haemolymph plasma from the wound and establish barriers against intruding microbes and other foreign bodies. It is suggested that the sequence of cellular events is similar in all kinds of lesions caused to the zygopteran integument, whether by ectoparasitic invasion or physical damage. It is likely that a resultant alteration in the properties of the subepidermal basement membrane will elicit the haemocytic response.