They're damaging your plant.

If you want to know how to manage them, drop into soapy water, or cut in half, or feed to the birds,.

Or take them to your county's Extension Service Office for ID in their
current condition. Locate our county's office by using this interactive
map - http://npic.orst.edu/pest/countyext.htm

If the only thing you want to know is who they are, rear them to adults. To do so, put several in a container with leaves of the same plant, add a porous lid, and wait til they complete their life cycle.

ThanK Jean - that is an interesting idea