apple tree has a hole in it
My very old apple tree has a large cavity in the main trunk, about 7 inches across and almost the whole width of the tree inside, probably where a large limb came off a long time ago. The cavity is full of water and there are large (1 - 1 1/2")white slug-type larvae swimming in it. I think they are living on the rotting wood. My question - has anyone ever seen this larvae before, and how do I seal up the hole? The apple tree is still very productive.