A female Ancisterocerus nigricornis  hunting on Dame’s rocket (Hesperis matronalis). They seek out their prey, larvae of small moths, in closed flowers. The caterpillars make a nest in the flower head by stitching the petals together. Within this enclosure they feed on the flower head.
The wasps patiently inspect all closed flowers heads by smelling them out and, when they suspect a prey inside, biting in them.
References1 Nederlands Soortenregister