I found this caterpillar on a birch tree. I think it is probably a Smerinthus sp. or Paonias excaecatus. I noticed that it had a dried frass stuck in/ on its rear. I tried to gently remove it with a pair of tweezers, but it did not seem like that was going to work. Another idea I had was wetting a tweezers with water and mashing the frass up until it could be wiped away with a paper towel. I have not tried the second idea yet. I have never seen an incident like this before. If anyone has any suggestions, it would be much appreciated.

Thank You.