Robots are supposed to run on batteries, right? Well not all of them.

Scientists in England have built a series of small robots that get their energy from dead flies, rotten apples, or sugar.

One robot, called Slugbot, was even designed to hunt garden slugs for dinner!

What's up with all that gross food?

Well, scientists at the Bristol Robotics Laboratory want to invent robots that can operate for long periods of time in dark, dirty, or dangerous places.

Many of those spots, like the seafloor or Antarctica, don't have electrical sockets.

So inventor Chris Melhuish came up with a better idea: Build robots that get their energy just like animals do—by hunting and eating food from their environment.

The robots digest their grub in a series of stomach-like devices called microbial fuel cells that are full of bacteria!

The bacteria do the real eating, munching dead flies or other food fed into the fuel cells.

As the bacteria chow down, they release electrons. Electrons are charged particles that flow to form electricity.

One robot, called Ecobot II, could run for 12 days on a diet of eight flies! (You'd still get a lot more power from one AA battery, though.)

Melhuish says his team is now working on a new and improved robot, called Ecobot III, which will have a better digestion system.

It seems that after an eight-fly dinner, Ecobot II couldn't get rid of the leftover "waste."

Maybe restrooms in the future will have signs for boys, girls, and robots.