We might rely on pyrotechnics to ring in the New Year, but the natural world has been producing eye-catching "fireworks" for millennia. In honour of 2017, we've rounded up some of our favourite luminescence displays!
Lady in Red
Measuring just 4.5 inches (12cm), the bloodybelly comb jelly (Lampocteis cruentiventer) glows boldly red. Red light doesn't penetrate the deep ocean, so crimson creatures appear nearly invisible in the depths. Scientists speculate that this jelly's red belly takes that camouflage tactic one step further by masking luminescence produced by swallowed prey. Those sparkling flashes you see come from light diffracting off hair-like "cilia" that beat to propel the jelly through the water column.
Like its cousin, the Portuguese man o' war, this glowing opalescent goo is no jellyfish. It's a siphonophore, a colonial cluster of tiny animals called zooids. This one was caught on film by the research vessel E/V Nautilus back in 2014 – but it's far from the only strange siphonophore that's caught our eye. From purple feather dusters to the orange oddball below, this group features some truly bizarre species.
It's not hard to see why insects in the genus Pyrophorus earned the nickname "headlight beetles" – but those bioluminescent light organs don't help them see in the dark. Instead, the spots lure in prey! Native to Central and South America, Mexico and the southwest US, the beetles' brilliance has inspired many a legend. In the West Indies, for example, lore has it that native peoples tied the animals to their toes to light their way (we don't recommend trying on beetle slippers, however).
Sun's Out, Buns Out
We couldn't leave these backyard beacons out, now could we? Fireflies might seem commonplace, but we're still learning a lot about them. In fact, scientists unravelled the secret to the insects' signature glow only in 2015. A firefly's abdomen contains oxygen and luciferin (a light-emitting compound), but those substances don't typically react when mixed – at least, not in a way that produces the light we see here. Research from Connecticut College showed that the oxygen in a firefly's backside possesses an extra electron, which changes the way the chemicals converse.
Swell sharks might not be as obviously impressive as their top-predator kin, but under blue light, we can see they have one heck of a party trick. Unlike bioluminescent animals, which produce light through chemical reactions, these sharks are biofluorescent. Special pigments allow them to absorb light in one wavelength, transform it and then re-emit it in a different wavelength (or colour). Swell sharks belong to the family Scyliorhinidae – a group known as "catsharks" – but over 180 fishes are known to fluoresce. It's thought these particular animals use DayGlo outerwear to advertise their whereabouts, perhaps during courtship.
Of the nearly 100,000 species of mushrooms, over 70 are known light-producers. The most widespread of those is Armillaria mellea, the "honey mushroom". Some bioluminescent fungi produce an all-over glow, thought to attract insects, which help spread spores. But honey mushrooms glow only beneath the cap, in the mycelium. Scientists believe that in this species, the light serves as a warning sign, a way to say: "I'm toxic, don't eat me."
Legs for Days
California is the only place in the world known to harbour bioluminescent millipedes (genus Motyxia), and like some fungi, their glow also serves as a toxicity warning. The bodies of these leggy critters are laced with cyanide!
But that's not all the glow the Golden State has to offer. During a rat census on Alcatraz Island, scientists discovered fluorescent millipedes as well. We still don't know why that species, Xystocheir dissecta, goes green, but the secret lies somewhere in its exoskeleton.
Cave of Wonders
A fungus gnat does not sound like a particularly alluring animal, but one particular species of fungus gnat found only in New Zealand has an illuminating secret: in its larval stage, Arachnocampa luminosa (also known as the glowworm) is capable of putting on a breathtaking light show. The blue-green glow is emitted by special organs in the gnats' tails, and it acts like a luminous lure for prey. Hanging from cave ceilings ensconced in silky tubes, the gnat larvae transform their subterranean abodes into star-speckled galaxies.
Son of Odin
Whosoever holds this hammer, if he be worthy, shall possess the power of Thor!
This crab might not be playing with a thunder weapon, but it is wielding something: a bioluminescent brittle star. Unlike true starfish (class Asteroidea), which mosey along atop hundreds of tube feet, brittle stars (also known as "snake stars") move quite quickly. But when the ability to make a quick getaway fails, some species can emit bright light from their long, flexible arms. It's thought the built-in flashbang scares would-be predators.
And speaking of quick getaways, this cuttlefish's sneaky escape is being foiled by its surroundings. While it looks like the creature is shooting light, it's actually activating bioluminescent plankton in the water. Many minuscule organisms (most commonly ostracods and dinoflagellates) glow brightly when agitated, and the cephalopod's jet propulsion stream provides enough of a shake-up to do the trick!
For the bloodybelly jelly we started with, red light's weakness offers a way to blend in against the ocean's dark waters. But on the flip side, many animals use bright blue light to stand out. Why? Let's take a look.
Some organisms, like the stunning comb jelly (Beroe spp) and Atolla jelly, use mesmerising ripples to ward of would-be predators.
"Fire-breathing shrimp", on the other hand, prefer to defend through distraction. When threatened, the animals squirt a cloud of light liquid that confounds predators while they make a getaway. The fluid is produced by an organ similar to our pancreas.
Every year, millions of firefly squid (Watasenia scintillans) gather in Japan's Toyama Bay to spawn. (You can see their tiny bodies moving here with the flowing tide.) Despite being just three inches (7cm) long, the creatures pull off dazzling displays that put others to shame. These squid use thousands of tiny light organs, called photophores, to attract potential mates and stake their claim against rivals during breeding events. Amazingly, the squid can control how their light looks: photophores can be flashed in unison or separately in an endless array of morphing patterns.
Though their dark bodies blend in against the black backdrop, the shiny lures of many deep-sea anglers bring prey within reach of their sharp teeth.
Animals like the strawberry squid (genus Histioteuthis) are particularly good at finding blue clues in the sea. That glowing, green eye is fine-tuned to absorb blue light, allowing the squid to detect the faintest changes in its surroundings.
Now you see me, now you don't! This underwater Houdini, colloquially known as a "sea sapphire", is a small crustacean (copepod) in the genus Sapphirina. Despite what your eyes are telling you, these animals are completely translucent (that's why they seem to disappear between flashes), but the males have a neat trick up their sleeves called structural colouration (more on that here). This results in the beautiful, vibrant colours you see here.
We're rounding off with the pièce de résistance: the fish that pukes up Patronus. Unlike the fire-breathing shrimp, this luminous spew is, well, actual spew. What you're seeing is a cardinal fish eating and then regurgitating bioluminescent ostracods.
Ostracods are planktonic crustaceans, typically about the size of a cucumber seed. To avoid becoming lunch, the drifters emit light-producing chemicals when ingested, which puts their attackers at risk of attracting predators of their own. The bloodybelly jelly may have found a way to hide its food, but cardinal fish are translucent, so if their meals glow, so do they. The only option is to release a glowing cloud of majestic egesta, and move along.
Top header image: Threthny/Flickr