An invisible force of nature, electricity is all around us. Humans generate weak electrical fields whenever we move our muscles, for instance. But some impressive animals have taken this power a step further, evolving the ability to communicate, defend themselves, and find food via electricity.
Most of such creatures live in freshwater ecosystems, using electricity to compensate for their poor vision or inability to see in murky water. Approximately 350 species of fish—including the notorious electric eel—possess anatomical structures that can generate up to a whopping 860 volts of power. In comparison, a shock from your household outlet its about 120 volts. (Read how electric eels hunt in the dark.)
Saltwater creatures, such as sharks, rays, and even one species of dolphin also rely on special sensory organs to hunt underwater. Though less common, land animals such as the bumblebee, platypus, and echidna harness electricity to forage and communicate.
Electrogenesis vs. electroreception
Animals use electricity in two different ways: electrogenesis (generating electric pulses) and electroreception (detecting these pulses).
“Electrogenic animals generate electricity and send it outside their bodies,” says Jack Cover, general curator of living exhibits at the National Aquarium in Baltimore, Maryland.
Such species include electric eels, torpedo rays, and African freshwater catfish, all of which send out high-voltage shocks to incapacitate prey.
Electroreceptive animals, on the other hand, can detect weak electrical fields generated by prey. When an electric field hits a living object, it creates a distortion that an electroreceptive animal can sense.
“This can tell them where obstacles or prey [or predators] might be, or even their size,” explains George Parsons, director of animal planning and dive operations at Chicago’s Shedd Aquarium.
Sharks are electroreceptive, seeking out prey using organs called the Ampullae of Lorenzini, which are concentrated around their heads. (Read how sharks can navigate via Earth’s magnetic field.)
“They can sense muscle movement as it puts out electric fields, especially drastic movements,” says Parsons. So a sick fish thrashing in distress, for instance, would be quickly discovered by a shark.
Some animals that are electrogenic, such as electric eels and the elephant-nose fish, can also be electroreceptive, using a small fraction of their electric ability to detect other animals in their environment while hunting. However, there are many electroreceptive animals that are not electrogenic.
Murky waters
For many animals moving through cloudy freshwater environments, charged electrical currents are as important as color or sound are to humans.
For instance, the electric eel’s habitat—South America’s Amazon and Orinoco River Basins—contains high amounts of sediment from the ever-shifting landscape.
That’s why the eight-foot-long animals—actually eel-shaped fish that belong to the knifefish family—are both electrogenic and electroreceptive. The species uses three sensory organs located along the length of their bodies to issue shocks of up to 860 volts—enough energy to stun predator or prey.
Each of these three organs—called the main organ, the Hunter’s organ, and the Sach’s organ—are made up of disc-shaped cells called electrocytes that have a positive and negative end, like the two sides of a flashlight battery.
“When a signal from the brain comes, these are discharged together and can act like millions of tiny batteries in series that form a massive jolt,” explains Parsons.
Such a defense mechanism comes in handy during the dry season, when water levels are low and large mammals are looking for food. If the fish senses a predator approaching, it may even leap out of the water to deliver an unpleasant surprise.
The electric catfish, found in Africa’s tropical freshwater environments, is capable of producing up to 350 volts to find food. The elephant-nose fish, native to West Africa, uses its electric tail to navigate murky waters. (Learn about Earth’s freshwater creatures at risk of extinction.)
Some fish also woo mates with an electrifying display. Both male and female ghost knifefish, native to South America, produce mild electrical pulses from an organ in their tails during mating.
These jolts help “coordinate and synchronize the release of eggs by the female, followed by the male’s release of sperm over those eggs,” explains Cover.
Shocking mammals and insects
While dolphins are famous for echolocation—the ability to locate objects by reflected sound—the Guiana dolphin, which can live in freshwater and saltwater, has evolved another strategy entirely: It detects prey by tuning into their electric fields, the only marine mammal known to do this.
In a 2011 study in captive Guiana dolphins, scientists found the animals had electroreceptor organs similar to those found in many fish species, as well as platypuses.
“It makes sense that this species would evolve this ability due to the turbid and murky waters of the western Atlantic coast of Central and South America,” says Tracy Fanara, an engineer and research scientist at the National Oceanic and Atmospheric Administration, based in Gainesville, Florida.
The platypus, native to Australia, is a semi-aquatic mammal that can detect prey via 40,000 electroreceptors in its bill. It uses this supersensory beak like a metal detector, moving it side to side as it swims to uncover crayfish and earthworms in the water.
The echidna, part of the same Monotremata family as the platypus and found in New Guinea and Australia, is possibly the only terrestrial animal to use electroreceptors to locate prey. The electroreceptive system in its fleshy snout is similar to the platypus, but far less complex, with fewer than 2,000 receptors. (Read about the silent decline of the playtpus.)
Among insects, bumblebees are known to alter the static electricity of flowers to communicate with members of their hive.
“Their wings are so fast that when collecting pollen, they actually create an electric field,” says Fanara. This can change the electric charge around a flower for about 100 seconds, communicating to other bees “that pollen from a flower has already been exhausted.”
Now, wouldn’t you like to know ahead of time when there’s no cake left in the breakroom?
