I noticed some large wasps going in and out of this hollow cavity in the Mimosa tree the other day. They are European Hornets (sometimes confused with Japanese hornets). They're about an inch long and lots of them. They will (so I've been told) completely destroy a hive of bees. So out came the spray and late evening I went out and sprayed the entrance. I also sprayed the following evening. Well, I still have these wasps going in and out. There must be a bunch of them in there. They're not aggressive (yet) and we've had rain so I'm gonna spray again in a couple more days.
There's always something going on with insects or varmints of some kind around here.