Someone's making homes in my American Elm leaves

[AndrewSmith]

Hi everyone

Any chance you know what this is?



There are tiny little worms inside, looks like they might have legs but I can't really see. But I accidentally noticed the big round thing on my finger as I was trying to make a photo:



There were also some (very few) small crystal clear balls inside the bad leaves. I don't know if they're all the same thing. Is it a caterpillar? Are they going to kill my tree? I just planted it. Should I try to do something about them?

Thanks in advance.

[PaulF]

It looks like galls formed by insects. Usually this does not harm the tree. Here is a better explaination:

http://www.extension.umn.edu/garden/ins ... ite-galls/