Caterpillar on the leaf of a weed beside the road. Although despised by up-country people for its uselessness, there is actually a lot of insects depending on the plant for sustenance during the dry season.
The weed is Indian Heliotrope, an introduced species. Folks from Philipines, where this is native, have discovered a number of significant medicinal uses for the plant, but Thais have not got onto that bandwagon yet.
This picture is one of series I have created from a short period of observing this weed during a recent weekend up-country...there is a gallery if you are interested, and I think it is one of my better collections.