Double trouble: Description of an attack on a nesting Delta sp. (Vespidae) by two Stilbum cyanurum (Chrysididae) cuckoo wasps

Cuckoo wasps (Chrysididae) are well known for their habit of laying eggs in other insects' nests, but the strategies by which they sneak their eggs into hosts' nests have seldom been described. I report observations of an attack by two Stilbum cyanurum (Chrysididae) individuals on a nesting Delta sp. (Vespidae: Eumeninae). The attack lasted over 1h 30 min and involved both S. cyanurum wasps simultaneously mobbing the Delta sp. in attempts to gain access to her nest. The mode of attack and oviposition are described, and details are compared with observations of attacks by S. cyanurum in other parts of its range.