caterpillars on violas

[ally866]

Has anyone grown Viola Friolina Cascadiz, a trailing viola?

Mine have done well in hanging baskets but I noticed a few days ago that quite a few flowers have been eaten. On closer inspection early this morning I removed 7 small dark brown caterpillars from the flowers and wondered if anyone else has had this problem and could offer some advice on what they are and how to get rid of them?

Thanks