Hamuli are hook-like setae on the anterior margin of the hind wing which interlock with the recurved posterior edge of the fore wing in the Hymenoptera during flight, making them functionally two winged. The possession of hamuli is an autapomorphy for the Hymenoptera. Three types of hamuli are distinguishable: basal hamuli, distal hamuli and secondary hamuli. Basal hamuli occur only in the Xyelidae, Pamphiliidae and Xiphydriidae. Secondary hamuli occur in two common forms in terms of their arrangement: openly spaced (dispersed) or clustered. Dispersed secondary hamuli are hypothesised as plesiomorphic and clustering is a putative synapomorphy for several groups within the order. Distal hamuli are present in all winged Hymenoptera. The presence of a modified and erect setal band opposing distal hamuli may be a synapomorphy for Chalcidoidea + Ceraphronoidea + Diapriidae + a new family to be described from New Zealand.