Electricity is the result of interactions between objects with electric charge – and batteries aren’t the only things that can be charged. Like the top and bottom of a battery, the inside of a living thing can have a negative charge while the outside is positive, or vice-versa, making it electric.
- How an electric eel works and the maximum shock it delivers... (you wouldn't want to be be hit by its deadly high-voltage charge)
- Meet these electric animals, from a ray that packs a deadly high-voltage punch to a species that uses electricity to communicate
What is electroreception?
Electroreception is the ability to sense an electric field, the physical forces produced by attraction and repulsion (electromagnetism) between charged objects, which spreads through a surrounding medium like ripples in a pond. In water, the charge across an animal’s surface interacts with dissolved molecules in the medium: opposite charges attract, like-charges repel.
Electroreception can be passive or active. For the passive sense, an animal detects electric fields created by other individuals (such as nearby predators, prey or mates) due to the charged surface of their bodies or muscle movements, which are controlled by electrical impulses and so affect the surrounding field.
How are electric fields detected?
An electric field is sensed via microscopic voltmeters called electroreceptors – pits in the skin connected to nerve endings – and perceived as patterns of voltage across the skin. In amphibians and fish, thousands of receptors (known as ‘ampullae of Lorenzini’ in cartilaginous fish such as sharks and rays) occur along the lateral line. Each pit leads to a canal filled with a conductive gel.
Which fish are electric?
Some fish are capable of active electroreception or ‘electrogenesis’. An animal uses a dedicated electric organ (modified muscle tissue, typically in the tail) to generate its own electric field by discharging the organ. Electric fish can detect distortions in their field due to the presence of other objects, via distinct receptors. This allows them to communicate, navigate and find food by electrolocation – useful if a species is nocturnal or lives in murky water. Fish with weak discharges (often less than 1 volt) rely on electrolocation, an ability that evolved independently in two families of bony fish: freshwater elephantfish and knifefishes.
Of more than 30,000 total species of fish, only the 350 or so that can generate fields are classified as ‘electric fish’. Passive electroreception, which occurs in 16 per cent of species, doesn’t count.
How do fish generate electric shocks?
Fish that deliver strong discharges can stun potential meals and enemies. Layers of fat and connective tissue help insulate their own bodies from the electric currents. The electric eel Electrophorus electricus (a knifefish, not a true eel like a moray) times shocks to trigger involuntary muscle contractions that reveal a prey’s location. This causes fatigue when an eel is wrapped around a large target. A sister species, E. voltai, holds the record for strongest generator of bioelectricity: it can deliver shocks of 860v, half the voltage of a taser.
Do other vertebrates sense electric fields?
Yes, a few mammals can use passive electroreception. In monotremes, receptors in the bill let a platypus detect prey in water (despite keeping its eyes, ears and nostrils closed), while echidnas may be able to locate insects by sticking their snout/beak into moist soil. In true mammals, at least one marine species – the Guiana dolphin – uses ‘vibrissal crypts’ (pits where they once had whiskers) as receptors for detecting electric fields, in addition to using echolocation.
Can invertebrates electrocute prey?
Scientists traditionally studied aquatic creatures such as fish because water is a good conductor of electricity, thanks to all the charged molecules it contains (water is rarely pure H₂O). By contrast, as a medium for electric fields, air is a poor conductor as its molecules are relatively few and travel fast. This is why the ability to detect fields isn’t common among land animals.
But recent studies have found that bees and other terrestrial arthropods have hairs or antennae that can detect electric fields in air: aerial electroreception. This is, if you’ll pardon the pun, an emerging field of research.
Read more of JV Chamary's columns
- How do birds, mammals and other animals navigate? Discover the incredible ways animals find their way around the world
- What would happen to the Earth if humans went extinct? Here's what scientists think
- Fight or flight response: what it is and why it's key for survival
- What and how do animals see? Mysteries of animal vision explained
