Currently there are many wasps in the garden. They fly on Trumpet vine and rotting apples but especially on grapes. Our grape plant produces masses of grapes every year and attract many birds and insects. Some of the insects drink the sap at the stems when the grapes are still attached to the plant. The wasps gnaw bigger holes in them to get to the contents. Grapes that have fallen onto the ground are completely emptied, sometimes with more than three wasps at the same time.
Update 7 september 2018:
As said the grapes are very popular with the wasps. I had created a feeding tray for butterflies but it is completely covered in wasps now so some divert to the fallen grapes.
Luckily they are social wasps….