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The worlds most electric animals

By Matilda Battersby

From electric eels to the execution chair, the story of electricity involves more than a shock or two.

So, just how did scientists use nature to harness this mysterious force?

We think of electricity as something man-made and modern. But, in fact, it exists in all of us biologically and it took the discovery of a fish capable of zapping us with 600 volts for us to learn how to generate it artificially.

That creature was the so-called electric eel (Electrophorus electricus), native to the Amazon River. This sizeable marine animal (technically a fish, often mistaken for an eel) can expend enough electricity to leave horses writhing in agony.

Its body contains three organs made up of electrolytes, or ‘battery cells’, lined up so that a current of ions can flow through them, and stacked so as to add power. Its biology proved so pivotal to informing human understanding of electricity that the inventor of the battery copied its formation.

There are very few electric animals and the majority of them are fish. The electric catfish is found in tropical Africa and the Nile River and can emit 350 volts. The electric ray, or torpedo fish, can produce around 220 volts and was documented by the Ancient Greeks and nicknamed the ‘numbfish’ because it was used as a basic anaesthetic in early medicine.

There are also animals that use electricity to help them locate prey or navigate in murky waters. Sharks are famously spectacular at electroreception, which is why they’re such good predators. If your muscles give off a spark of electricity (which they do if you’re alive), sharks will find you.

Most electroreceptive animals are water-dwellers. But there are a limited number of electric mammals, such as the land-dwelling echidna (sometimes known as a spiny anteater), and its cousin the duck-billed platypus, which lives both in water and on dry land.

"It's possible that lots of aquatic animals use electricity in ways we don't understand."

Both the echidna and the platypus have tiny electroreceptors on their snouts (up to 40,000 in the case of a platypus), which detect currents and allow them to burrow through silt or dry land and locate prey with their eyes closed. The echidna’s electrical capabilities are all the more remarkable for being on land. More recently, a species of dolphin, the Guiana dolphin (also technically a mammal), has also been found to use electroreception.

On dry land, the honeybee is known to beat its wings at such a fast rate that it generates an electrical charge, which is then transferred to a flower when it is pollinated. Another bee can therefore detect the presence of an electrical charge if visiting the same flower, and it tells them not to bother foraging there. ‘It’s possible that lots of aquatic animals, possibly other mammals, use electricity in ways we don’t understand or haven’t logged,’ says Jack Ashby, manager of the Grant Museum of Zoology at University College London. ‘Because humans don’t do it, we don’t pay quite enough attention to it.’

The fact that we paid attention to the electric eel is a testament to the shocking strength of the impulses it could discharge. In their native South America, electric eels had been known about for generations and some early experimentation began in the 1700s. But in Europe and North America they were akin to mythical beasts, like unicorns.

More broadly, at that time, electricity was viewed as a phenomenon. Events such as lightning were seen by Medieval and Renaissance-era humans as some miraculous, unseen occult thing like magic or God’s wrath.

The shock of the new

When naturalists first heard about electric eels in the mid-18th century, a time when Benjamin Franklin was experimenting with lightning rods, the discovery sent a charge of curiosity through the scientific community.

‘The eels were sent to North America and London, where they became part of this whole scientific spectacle that was then building,’ says Ruth Garde, curator of the Wellcome Collection’s new exhibition Electricity: The Spark of Life. ‘They were put on display in theatres and were billed as wonders and marvels of electricity. People paid huge amounts to see them.’ In those days, the term ‘electrician’ was used to describe the scientists who were interested in electrical experimentation. As part of their investigations, electricians collected electrical charges in Leyden jars (literally glass jars with metal lining), which occasionally gave them nasty shocks. The scientists were focused on trying to prove the existence of atmospheric electricity.

The study of an animal that could, at will, produce more volts than humans could store in a jar, proved to be a huge help in advancing their understanding.

One of the earliest (and most dramatic) reports of electric eels to reach Europe was from the Prussian naturalist Alexander von Humboldt in around 1800. He visited what was then Dutch Guiana, the region between the Orinoco and Amazon rivers in South America, and described seeing eels emitting such high voltage that they were feared as monsters in the local area.

Humboldt describes the ‘picturesque spectacle’ of fisherman driving horses into a swamp to be shocked by the eels in order that, once their electricity had been discharged, they could be safely scooped up for study and experimentation. ‘Some of these horses were injured or dying and the native fishermen kept them in the swamp… It’s quite a gruesome story, but the way [Humboldt] writes about it is very compelling,’ says Garde.

Highly charged rivalry

But the arrival of the electric eel in America and Europe wasn’t just the biggest electrical event on the block. ‘The electric eel was critical in our understanding of how to develop electrical currents for our own use,’ says Garde.

Alessandro Volta, the Italian physicist who invented the electric battery (or Voltaic pile) and after whom the unit of electric potential is named, based his work on the anatomy of the electric eel. ‘Volta called his earliest device an “organ” – a direct reference to its biological roots,’ Garde says. In fact, the invention of the electric battery was an unexpected but happy consequence of Volta’s research into the then controversial subject of animal electricity. He had been a critic of the 1780s experiments of Italian physician Luigi Galvani, who connected the nerves of a dead frog to a metal wire and pointed it toward the sky during a thunderstorm. The frog’s legs twitched as if it were alive.

While Volta and Galvani were debating whether electricity came from biological or external sources, Mary Shelley was so intrigued by the notion of a spark somehow reanimating the dead that it would inspire her to write Frankenstein.

Galvani later proved, conclusively, the existence of internal animal electricity. But his work did not succeed in convincing Volta – who objected to the notion on religious grounds. Galvani’s theory was largely ignored by the scientific community until his experiments were picked up again decades later, according to Marco Piccolino, the co-author of The Shocking History of Electric Fishes. Modern science accepts that all muscle cells, human or animal, have electrical potential. A further two centuries of experimentation have confirmed that muscle contractions are initiated by electrical-nerve impulses and that a potential electrical energy is present across the membranes of all cells. Why are some animals more electric than others? It seems to be a quirk of evolution that certain muscle cells changed over millions of years into electrocytes generating much higher voltages than ordinary muscle cells.

‘Electric fish fed our understanding of what electricity is,’ says Garde. ‘It led to our understanding that electricity is in our body, how it works through our bodies and how it might be sent through the body to help it.’

Photograph © Vladimir Wrangel

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