Welcome to the second instalment of the April Fool’s Day Files, where we celebrate the conniving con artists, tantalising tricksters, and devilish deceivers of the natural world. This year, Natural History curators Phil Sirvid and Thom Linley illuminate how animals lie with light. The bioluminescent light some animals make is a chemical reaction of luciferin, named after Lucifer, the Lightbringer, the Great Deceiver, and the Father of Lies, it’s time to trick with light!

Fireflies or Fire-Lies?

Despite their name, fireflies are not flies, but bioluminescent beetles. While we don’t have them in Aotearoa, their nocturnal light shows are well-known in many other countries. Firefly mating can literally be a tricky business. Each firefly species has its own flashing light signals to help males and females recognise each other so they can come together and mate.

However, females of some species copy the signals to attract males of other species, and it’s not for mating. Deceived males are killed and eaten by these hunting females. Males aren’t just tasty snacks, though. They are also a source of defensive steroids that the females can’t make themselves. These chemicals can make a female and her eggs toxic to predators. While a predatory female can metabolise and incorporate these toxins safely, anything attempting to eat her afterwards is going to regret it!

The deception isn’t always one-way. Some males can lie just as effectively as females. When a femme fatale flashes her photonic falsehoods, he may signal back that he’s the prey species she is trying to deceive. She ends up with a potential mate rather than the chemical banquet she was hoping for.

The Spider with the Night Light of Doom

Chinese Scientists have discovered an orb weaver spider that can use captured male fireflies to attract even more of them to its web. Normally, the spider would just wrap its prey in silk and bite it before feeding, but if the spider senses it has caught a male firefly, possibly from detecting its light, it does something different. Once the firefly is secured in the web, the spider makes the male firefly flash like a female well enough to attract more males. Quite how the spider does this is not yet known. It may be the physical act of biting, or it may be something in the spider’s venom. Whatever the case, that the spider is somehow able to subvert the firefly’s signalling ability and use it for its own ends is simply brilliant.

Just how do animals make light?

Whether it’s a fish, a firefly, or the good old New Zealand glowworm, animals that  can make light all use a similar chemical reaction. The formula requires calcium, adenosine triphosphate (ATP), and the chemical luciferin, and adds oxygen and an enzyme called luciferase. When these come together, hey presto, the reaction releases light, and fortunately for the animal, not much heat.

Into the deep

In the deep sea, where there is very little or no light from the sun, most animals produce their own. Due to the huge size of the deep sea, bioluminescence is the dominant form of communication on the planet. When you control both sides of the equation – both the light and the thing being observed, you can tell a lot of lies; the big can appear small, the small can appear big, nothing is quite what it seems.

A tasty little fish

In the twilight zone (the mesophotic) there is just enough light to pick out silhouettes of animals from below. Many animals make light on their undersides to cancel out their shadow, but the cookie cutter shark (Isistius brasiliensis) takes it one step further. They have a dark collar that looks a lot like a smaller fish. When a large predator charges up from below to eat it, the shark does a pirouette and takes a chunk out of the larger predator. The perfectly round holes they leave behind give them their name.

Sniper scope

Blue-green light travels best through water. Most bioluminescence, and deep-sea eyes, operate in this wavelength and the animals are often totally blind to other colours. The stoplight loosejaw (Malacosteus sp.) takes advantage of this. They can make and see red light. They can shine a spotlight on their prey that only they can see.

Shoulder-mounted smoke grenade

The tubeshoulders (Platytroctidae) are a modest looking family of fish, black/brown in colour, with a few light organs on their underside to break up their shadow – the standard dress code in the twilight zone.

They do have a neat trick up their sleeve though, a modified tubular scale on their shoulder (if fish had shoulders) leads to an internal pouch of bioluminescent material. When startled, the fish can fire this shoulder mounted RPG and eject a glowing smokescreen like a squid releases ink. This will blind and disorientate the attacker but also lights them up. There’s always a bigger fish, and in the deep sea, being seen is a great way of getting eaten. The tubeshoulder tags the target and calls in the underwater equivalent of an airstrike!

Luciferin and luciferase started off as a way of bacteria detoxifying oxygen, before things even had eyes. It didn’t matter back then that it kicked out a few photons of light, no one could see them. Now that the animals have gotten hold of it, it may look beautiful, but it’s often devilishly deceptive and deadly.