These seem to have moved into the base of my willow tree and i am worried that they might be harming the tree. can you tell me if i need to take measures to discurage them from my tree.
Your wasps are Cicada Killers and there is no need to worry about them harming your trees. Adult wasps feed on nectar and pollen and the female stings and paralyzes cicadas to provision a solitary underground nest for her young. Cicada Killers help control the Cicada population, and Cicadas may harm your trees by feeding on plant sap at the roots when they are immature. Additionally, the female damages twigs when laying eggs, so the presence of Cicada Killers may benefit your tree. We have gotten reports of large colonies of Cicada Killers frightening people, but they are rather benign insects, though the occasional sting is reported to be painful. While it is interesting that you have titled your photograph “Nasty New Freeloaders” we feel the name is unjustified.