Twelve larvae of Ascalaphidae – in four similar forms – were found in different regions of Costa Rica. Behaviour and external morphology are briefly described. The flat larvae are camouflaged in coloration and exceedingly inactive. They spend weeks sitting on the surface areas of large leaves where, in a cautiously selective manner, catching insects which are climbing past them. The larval development takes between one and two years. Larval rearing was only successful in the case of Haploglenius luteus Walker, 1853.