The reproductive behaviour of I. graellsii in a high-density population at Lourizàn (Pontevedra, Spain) and under laboratory conditions was studied. Copulation duration varies between 74 and more than 250 min. Stage 11 lasts for 2-8 min and takes place 12.6+0.84 min before the end. Oviposition is made by unaccompanied females, usually in the morning, before the initiation of reproductive activity (94% of copulations take place between 1:30 and 5:30 h after solar noon). It has been shown that andromorph females are not recognized as females by males. Such females mimic the behaviour of males and, in the insectary, rarely copulate twice in the same day, as is usual for heteromorph females. The high morphological and behavioural similarity between /. graellsii and I. elegans, and the fact that copulation between male /. elegans and female /. graellsii is possible indicate that they may be sibling species.