Ectemnius

thumb|Ectemnius maculosus thumb|Ectemnius cephalotes at a nest entrance Ectemnius is a genus of wasps in the family Crabronidae. 188 species are known. The genus is found around the world but Australia has only two species.

Ectemnius species excavate nest tunnels in pieces of dead wood such as stumps, fallen tree trunks, rotting logs and sometimes building timbers or posts with the help of the mandibles. Nesting aggregations can be large and dense, and sometimes more than one female has been recorded using a common nest entrance. In most species the brood is supplied with Diptera from several different families.