What is hiding under the bark?

What is hiding under the bark?

Patient 11-2015, a Brown Bat, is recovering after a fall into water. The wing graciously displayed for the photo is composed of fingers with a membrane between.
Some bat trivia:
70% bats are insectivores
They can migrate, hibernate or place themselves into torpor.
Their baby “pup” at birth can weigh 25% of the mother. That is big!
They can eat 1000 insects/hour