Earth Hour is a global event organised by World Wildlife Fund (WWF) where individuals, businesses and communities switch off non-essential lights for one hour to raise awareness about climate change and environmental issues.

Held annually, it aims to inspire collective action for a sustainable future by highlighting the importance of energy conservation and reducing carbon footprints.

This year, Earth Hour starts at 8:30pm on Saturday 22 March. People around the UK can settle in for the hour by switching off lights and getting their daily dose of nature at home. 

However, while the lights go out in towns, cities and households around the world, many non-human species are creating a glow of their own, using bioluminescence to attract mates, distract predators and shine in the dark.

Here, we reveal some of the world’s most remarkable bioluminescent creatures ahead of this year’s Earth Hour.

Found over 500m deep in the North Atlantic, the glowing sucker octopus is one of the few bioluminescent octopods in the world.It’s believed to use bioluminescence to scare off predators and also lure in the tiny planktonic shellfish it feeds on.

Sea slugs, or nudibranchs, can be found in oceans across the world and there are over 100 species in the UK. These bright and colourful molluscs, such as this stunning butterfly nudibranch, can emit light to distract and startle predators.

Native to the east coast of America, the warty comb jelly or sea walnut has become invasive in European waters. Many jellyfish, including the warty comb jelly, use bioluminescence to evade predators, either flashing light to startle them or to attract larger predators that may attack their attacker.

Unlike their winged adult form, firefly larvae sometimes referred to as glow-worms use bioluminescence to suggest to potential predators that they don’t taste very nice. They’re also merciless predators themselves of slugs and snails, injecting their prey with a paralysing venom before dissolving their bodies with regurgitated digestive enzymes.

Fireflies, also known as lightning bugs, candle flies and fire beetles, are found in temperate and tropical regions around the world and are one of the most recognisable bioluminescent species. It has been suggested that the ancestors of fireflies originally used light to ward off predators, but today it’s more commonly used to attract mates.

Antarctic krill number over 700 trillion and their ‘super-swarms’, tens of thousands of kilometres wide, can be seen from space. These krill use bioluminescence to camouflage themselves from predators and communicate in their great swarms.

Main image: warty comb jellyfish (Mnemiopsis leidyi) floating in the water, Egersund, Naalaugvika, South West Norway/Credit: Erling Svensen / WWF

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