Either snails or slugs. Try Diatomaceous Earth or wood ashes. The sharp substances in both irritates - rips - their slimy bodies, and they won't crawl over it. I've used DE on aphids, too. Works like a charm. Also - and here's a strange remedy - I tried hanging banana peels from the branches of my peppers (for an aphid cure), and that worked, too! Apparently, decomposing banana peels emit some kind of chemicals the aphids disdain. I wonder who figured that one out... !! R.