From Sonic Retro
It's a crab-like robot that leak out from wall shutes. In many places, it is said that they spawn infinitly. However, this is a false statement. They DO stop spawning, but it takes a while for this to happen. If you have the time and patience to kill them off, eventually they won't spawn anymore. Again, it takes a long time, but you can kill them off in the areas in which they are located. If you are going for score attacks, this is a great way to boost your score.
They crawl slowly while they don't detect an enemy, but will quickly swarm in when in line of sight and set to self-destruct when they are very close. They appear in Final Egg for Sonic.
On a small note: Beats don't drop animals when defeated, suggesting that they run off a different power source. However, this is most likely so that the player cannot "farm" for animals, due to the near infinite numbers of Beats. The fact they explode quickly after being deposited is probably the result of having no organic battery.