These wasps were actively hunting on aphids on Common dogwood (Cornus sanguinea). As Pemphredon lugubris was also present on the plant I erroneously assumed these hunting females were the same species. Pemphredon hunt on aphids as well . However when processing the photographs it became clear this was a different species, Psenulus pallipes , a new garden species!
The wasps used the high to middle-high parts of the plant as their hunting ground.
They were aiming the Anoecia corni aphids that occupy the plant in large numbers and are under constant protection of the Jet ants (Lasius fuliginosus) whose nest seems to be located in the ground between the plant’s roots.
The large wingless aphids are the wasp’s target. The winged variant appears later in the year.
The wasps approach the protected aphids carefully floating next to the leaf or twig the prey dwells on, prying for an opening in the ant defences. The fact they are so careful probably means the ants are a potential threat capable of injuring the wasp. When the wasp approaches, the ants start moving excitedly. The ant defences do function well looking at the time the wasp needs in order to succeed in catching a prey. She will hover up and down the leaf or twig looking for an opening. A large number of the attacks will fail.
When the opportunity reveals itself, she bolds forwards, grabs the prey and flies away to land on a leaf a bit further away. I’m not sure what they were doing, it seemed she was just taking a moment to take a small break before returning to the nest.
References1 Nederlands Soortenregister