Thank you for your question. I hope the information provided below will help you better understand what is happening to your maple tree. I have also included additional resources in case you want more information.
Part 1: Green Substance
From the pictures you sent, the green substance on the tree appears to be moss, or lichens. It has the right consistency and color. (See reference pictures) There are a variety of conditions that favor moss, or lichens growth. These conditions are:
- Moist climates – sides of the tree that faces the wind and rain
- Overcrowded branches
- Parts of the tree that do not get a lot of sunlight
- Cooler parts of the tree
- Older trees
- Prune the trees to allow for more direct sunlight
- Aerate the lawn to prevent puddles from forming around the base of the tree
- If you have an irrigation system in your yard, be sure to direct the sprays away from the tree.
Part 2: The Holes and Insect
The next part of your question asked about holes and the insect that you were seeing on your tree. It looks the holes and the insect are actually connected. Another insect known as the horntail wasps drills holes into the dead tissue of trees to deposit their larva. Along comes the wasp that you have been seeing, the ichneumonid wasp. The ichneumonid wasp will then tap along the tree to find the larva burrowed below the surface. Once located, the ichneumonid wasp will drill deeper into the tree to locate and deposit their egg on top of the larva. All of this information leads to the conclusion that the presence of the ichneumonid wasp means that your maple tree may be dying. It would be best to bring out a tree care professional that is experienced in diagnosing tree insect pests or diseases and tree health diseases to take a closer look at your tree. I do want to mention that the wasp, although scary looking is harmless to humans.