Did you know you can make a simple computer out of a swarm of soldier crabs? I sure didn't, and I'll bet you a fresh seafood dinner that the crabs themselves had no idea either. But some enterprising researchers from Japan have shown that it is possible to make a crabputer. Practical? Maybe not so much.
Yukio-Pegio Gunji and his colleagues from Kobe University in Japan somehow figured out that when two swarms of soldier crabs run into each other, they merge into one single swarm that continues moving at a speed and direction that is the sum of the velocities of the two original swarms. For the crabs, it's just an instinct, but that instinct can be harnessed to create a very primitive sort of computer that can perform logic operations.
By "logic operations," we're talking about seriously basic stuff called boolean logic. Bits of information (the equivalent of ones or zeroes) are sent through "logic gates" which combine two bits in a logical operation (like "AND" or "NOT") that generates an output. In this particular case, the input is swarms of crabs, the gates are physical gates, and it's the vector of the swarm that performs the operation. Here's what the crabputer looks like:
To get crabputer to work, swarms of 20 crabs are loaded into the input spaces behind the gates and allowed to relax. After a few minutes, the gates are opened, and "intimidation plates" (red pieces of paper that cast shadows over the crabs) are placed behind each swarm to cause them to move along the corridors. In the event that the computer is attempting to perform an "AND" operation, the two swarms of crabs collide, and the majority of them change direction and drop into the "AND" bucket (labeled 2 in the image). Or at least, that's the idea. So far, the crabs aren't super great at pulling off an "AND" operation, but are much better at "NOT" and "OR."
You can also do collision computing like this with billiard balls and other things, but the advantage of using swarms of crabs (and the point of this research, apparently) is (as far as I can tell) that a biological swarm is more robust and resilient to perturbations. Or something. The disadvantage, of course, is that you have a computer that's freakin' stuffed full of crabs.
Just one final note, from the paper:
"The duration of any single experiment was so short that each crab never reached dangerous level, that the crabs were kept in comfortable condition, and that after all experiments the crabs were released to their natural habitats. Furthermore, on visual inspection, no crabs appeared to have been injured or adversely affected by the experiments."