Animal Senses #11: Electricity

Electricity. Species like the electric eel use it. But for humans to understand them, they had to first discover and learn about the concept of electricity, explains Ed Yong in Immense World! In fact, the study of electric fish is intertwined with the study of electricity. They inspired the design of the first synthetic battery. And fuelled the discovery that muscles and nerves run on electrical currents.

 

The electric organ on the fish’s tail is like a small battery. It creates an electric field around the animal. Current flows from one end of the organ, through the water, to the other end. All living things nearby act as conductors and increase the flow of current, while insulators (like rocks) reduce the flow of current. These changes affect the voltage on different parts of the fish’s skin. To draw an analogy with our sense of vision:

“Conductors shine brightly… insulators cast electric shadows.”

 

Electric fishes use electricity for locating things. But, unlike light, they need to generate the electricity themselves. And unlike the way bats use sound, electrolocation is instantaneous. It is also omnidirectional. Which, by the way, is why electric fish can detect things behind them. A constraint is that the electric field is often weak, and so it can only detect things nearby.

“Stillness, concealment, and silence don’t work against electrolocation. To an electric fish, all that’s alive stands out against all that isn’t.”

 

Electric fields are also used for communication. By adjusting the field strength, information is passed onto its fellow species members.

 

Since all living things have electricity moving through them, they create very weak electric fields around them. But at certain body parts (mouth, anus, and wounds), the field strength is a bit stronger. Predators like sharks can detect the slightly stronger field and zero in on their prey. Sharks then are passive electroreceptors – they don’t produce their own electricity, instead they detect others’ electricity. “Stillness, concealment and silence” don’t work against electroreceptors – after all, no living thing can stop producing an electric field.

 

Electricity is probably the only raw and un-translated sense out there:

“The language of the brain is electricity and… animals have evolved weird ways of converting light, sound, odorants and other stimuli into electrical signals. But electroreceptors are just translating electricity into electricity.”

 

Electroreception has a key limitation: it only works when immersed in a conductive medium. Like water. Not air. Which is why almost species that use electricity for any purpose are almost always aquatic. Note I said “almost”.

“The air carries a voltage of around 100 volts for every meter off the ground.”

Not a typo – it is indeed that much. Which means there is a slight potential difference between flowers close to the ground vs bees flying the air.

“When positively charged bees arrive at negatively charged flowers, sparks don’t fly, but pollen does.”

Not only that:

“Based on its shape and size, every flower is surrounded by its own electric field.”

And yes, bees can detect those fields and use it as information.