I have a huge California willow tree in my yard and have noticed a hole the size of a basketball. The hole is near the base of the tree approx. 5 inches from the ground. There are ants crawling in the hole but no other insects that I could see. There is something that looks like sawdust but not a lot of it. Is this something I should be concerned about?
I would recommend having the tree inspected my a qualified Arborist.
You need to determine if these are carpenter ants, as they could damage the tree beyond repair.