Electricity is something we rely upon on a daily basis, but what if we could manufacture it inside our own bodies? A surprisingly long list of animals is capable of doing just that… although not necessarily the ones you might expect.
Bioelectrogenesis is the term for electricity generated by living organisms. It therefore includes nervous impulses, cellular metabolism and photosynthesis – which means almost every living on Earth is able to generate electricity. But the quantities involved in those examples is tiny. What about animals that can generate a bit more voltage?
- Electric Eel
Pleasingly, the Electric Eel (Electrophorus electricus) is one animal that lives up to its name. Well, sort of. It’s not really an eel, it’s a relative of catfish, but it is . Electric eels freshwater fish found in rivers and lakes in South America. They are able to generate burst of electricity up to 860 volts, which they use for hunting, self defence and even communication. They mostly use low voltage pulses to help them sense their environment. But the shocks could be strong enough to cause heart failure (after repeated hits), and although deaths due to electric eel shocks are rare, they are not unheard of. After multiple strikes, electric eels get worn out, and cannot continue to produce electricity. But electric eel bodies can still produce a shock up to 8 hours after death!
- Electric Catfish
Electric eels aren’t the only fish producing electricity. Lesser-known electric catfish (order: Siluriformes) are close relatives of the electric eel (which is actually a knifefish), and include 19 species of electricity-generating fish. Found in Africa, electric catfish are capable of producing electric shocks of up to 350 volts.
- Elephant Nose Fish
Another brilliantly named fish, the Elephant Nose fish (Gnathonemus petersii) actually has an elongated chin (not a nose) called a Schnauzenorgan. The Schnauzenorgan adds a new sense – the ability to detect electric fields – which the fish uses to find prey. It generates electrical pulses from its tail, which radiate out into the environment much like a bat call. The fish then uses it’s Schnauzenorgan to detect changes in the electric field caused by prey moving around nearby. This highly sensitive organ can identify a living beetle from a dead one through 2 centimetres of soil!
- Electric Ray
Electric rays or sting rays (Order: Torpediniformes) is a group including over 60 species who possess special organs, imaginatively called electric organs, which are capable of generating electricity up to 220 volts. They use electric shocks to hunt prey and defend themselves against predators. Rays have good control over the strength of their electric shocks, using low-voltage shocks to warn off predators and higher-voltage zaps to stun prey.
- Atlantic stargazer
The Atlantic stargazer (Uranoscopus scaber) is a spiny fish found on the sea floor, where it uses bioelectrongenesis to shock and immobilise prey.
- Black Ghost Knifefish
Another relative of the electric eel, the eerily-named black ghost knifefish (Apteronotus albifrons) is a nocturnal freshwater fish found in South America. It is commonly kept as a pet because of it’s dark, mysterious appearance. They are capable of producing weak electrical pulses from their tail, which, much like the elephant nose fish, it uses to detect nearby food.
You might expect jellyfish to be electric, but they’re not! The sting of a jellyfish is caused by specialised cells in their tentacles called cnidoytes. Cnidocytes contain nematocysts, harpoon-like structures containing venom, which penetrate skin extremely fast. The nematocysts inject venom into the skin causing a painful rash.
- Oriental Hornet
The Oriental Hornet (Vespa orientalis) is the only invertebrate example here capable of bioelectrogenesis, and it is quite remarkable. Inside her abdomen are specialised cells that absorb sunlight and convert that solar energy into electricity. These form yellow and brown stripes on the outside of her abdomen – yellow absorbs sunlight, brown makes electricity – which can absorb 99% of light that hits them. The solar-powered hornet can then produce energy directly from sunlight, explaining why these hornets, unlike most insects, are moreactive during the hottest part of the day. Scientists are still unsure exactly what the hornets are doing with the electricity – it may provide a back-up store of energy for flight or to stay active when the weather gets cold.
Fireflies (Family: Lampyridae) are a group of beetles capable of making a glowing light in their abdomen. But this is not an electric light, it’s a chemical one. The light produced by fireflies is generated when oxygen mixes with the pigment luciferin, the enzyme luciferase and ATP, which provides cellular energy. Fireflies use their flashing light to attract a mate.
- Annoyingly, I can’t find a tenth, so you’ll just have to settle for nine.
So most of the genuine electric animals are in the catfish and knifefish order (Gymnotiformes), but never-the-less, scientists believe that the organ used to produce electricity in these fish, known as a myogenic electric organ, has evolved independently six times in different species. Even more surprisingly, despite distinct evolutionary histories, the electric fish all seem to utilise the same genetic and cellular machinery to achieve their goal of bioelectrogenesis. Interestingly, while the list of animals that can generate electricity is relatively short, a surprising number of species can detect electric fields in their environment, including bees, dolphins, platypuses!
Want to Know More?
- Gallant et al (2014) Genomic basis for the convergent evolution of electric organs Science
- Solar energy harvesting in the epicuticle of the oriental hornet (Vespa orientalis) Naturwissenschaften