I think lighting could be tweaked to better emphasize the snails. The highlights on the leaf compete for my attention, and the detail in the background distracts somewhat as well. I don't have a specific idea because I'm no lighting guru, but it just seems that the snails are too close in visual strength to the surrounding details to make a strong subject. It is a creative idea though!
Very cool, these guys must be trained well, if I had one around here, I would have put a postage stamp on it for the communication challenge and called it "Snail Mail". Great work.