3/4" holes are cause for some concern. The most likely cause would be a
carpenter bee, but you might want to also check into the Asian
Longhorned Beetle which is a serious threat to trees now.
When insects pupate they leave bits of silk and the like behind.
The carpenter bee is not a serious problem as it only makes a home .
The asian Longhorn Beetle is a tree killer because the larvae girdle
the tree under th bark.