I found these caterpillars on Water Mint growing in my garden pond. The bottom two images show early stage larvae which I discovered on my shed wall. Note the difference in colours.
The larva feeds on the leaves and flowers of various species of mint, including wild and cultivated varieties. They also feed on Marjoram, Dead-nettle, and other Labiataes and herbs. More mature larvae spin a web, a silken retreat, on the foodplant from which they feed.
They are seen June and July, and into the autumn. The autumn generation hibernate in their cocoons
See about adult here.
© Pete Hillman June and September 2017.