A fellow EN Worlder pointed out an article on Wired.co.uk from early 2010 that I had missed which shows design work on robots meant to convert organic matter such as insects and even rodents into energy for power cells. The one pictured below is based on the idea of a pitcher plant. To quote the narrator of the accompanying video, "Each robots will evolve over time by both its programming and owner interventions as the host develops a relationship and understanding of the robot's requirements, perhaps moving it from room to room or even feeding it artificially when energy levels are becoming low." Sounds a little ominous. See more here!