Hi Mary, thanks for the question.

I sent one of the pictures to MSU to their diagnostics lab and the bug guy their indicated it was probably a beetle larvae but did not know what it was.  The smaller ones are just less mature.  The weird stuff the bigger ones have on their backs is most likely a "fecal shield" to protect it from predators.  My personal research indicates this may be a leaf beetle in the Blepharida group. Hand picking and putting them in soapy water can work.  Spinosad or Sevin will also work while they are feeding. 

You can send some in to the MSU Plant and Pest Diagnostics lab:

• https://www.canr.msu.edu/pestid/

Be sure to read the "Submit Sample" page.

I would appreciate it if you could send clear closeup view of the pest.   I'm determined to find out what it is.

I hope this helps.