Wasp behaviour

[Bluejemsa]

Since we pruned two willow trees near our garden pond last month, hundreds of wasps and a few flies are flying around the trees, and crawling along the trunks and branches, and over the plants on the ground beneath the trees. No sign of a nest, and no obvious flight paths. Wasps are not stripping wood from tree. What ARE they doing? Hope someone knows!

[Jules001]

I can't say for sure, but it sounds to me like when pruning the tree you released sap from the branches, which may have dripped onto the ground below and the wasps and flies are attracted to the sweetness of the sap, the flies may just be attratced to the moisture though.

[lindisfern]

They are probably looking for grubs, different kinds but
mainly eggs are laid in tree bark grubs hatch and migrate
to form galls sometimes in the leaves themselves also
creating round galls attached to branch stalks. Cut one open
usually find quite a large maggot thing inside.
Wasps also patrol in late summer for caterpillars,not sure how
they do it but they seem to glue the hind end of the caterpillar
to stone or branch, cut a bit of to take away leaving the living caterpillar stuck until the whole caterpillar has been disposed of. Please note, these are observations from my garden not science fact.