Not all computers are made of silicon. By definition, a computer is anything that processes data, performs calculations, or uses so-called logic gates to turn inputs (for example, 1s and 0s in binary code) into outputs. And now, a small international community of scientists is working to 
expand the realm of computers to include cells, animals, and other living organisms. Some of their experiments are highly theoretical; others represent the first steps toward usable biological computers. All are attempts to make life perform work now done by chips and circuit boards.
Last year, for example, a computer scientist at the University of the West of England named Andy Adamatzky and a team of Japanese researchers built logic gates that ran on soldier crabs. First they constructed mazes that replicated the shape of the wires in a computer’s logic gates.
Then they chased two swarms of crabs (inputs) from one end of the gate to the other. When the swarms collided, they combined to form a new swarm (output), which often headed in the direction of the sum of their vectors, demonstrating that a living, somewhat random system can produce useful order.
for more here . About biocomputers , it’s a extremelly interesting topic . Actually this video demonstrates a biocomputer you have to see this :
zeracuse 