Very strange leaf markings
 

I can not find a reference to this anywhere, so I'm hoping someone can
help me. My umbrella tree leaves have developed slash-like marks
almost as if someone cut them with an exacto knife. The slashed part
hangs on by a thread, turns black and then falls off. The cuts
(chews?) can be found in old and new leaves. Is there some pest that
does this sort of damage? Or do I have a night-time, knife-wielding
intruder to worry about?
Thanks for any help!
Samantha