Buzz
Bioluminescence, the light emitted by living organisms, can be mesmerizing. The gentle radiance of fireflies in the night sky is a well-known sight around the world, yet not all bioluminescent phenomena are as serene.
While fireflies use their glow for signaling and attracting mates, bioluminescence doesn't always serve as an invitation. In some cases, it functions as a distraction or a method of concealment.
The natural world is a battleground, and any edge can mean survival or demise. Here are 10 examples where biological light helps animals in their strategies for defense and deception.
10. The Illuminated Jets of the Pocket Shark
In a fortunate twist of fate in 2010, researchers studying sperm whale feeding in the Gulf of Mexico stumbled upon a specimen from an entirely new species of pocket shark. These tiny sharks measure only 14 centimeters (5.5 inches) in length.
This specimen wasn't identified as a pocket shark until 2013 when further examination of the collected samples took place. It’s an understandable mix-up since the only other known pocket shark species resides in the Pacific Ocean, not in the Gulf of Mexico.
Among the 500 or so shark species worldwide, this newly discovered one possesses a rare ability. Located beside its two front fins are pouches filled with bioluminescent fluid. When released, this glowing substance creates small bursts of luminous . . . squirt.
The pocket shark utilizes these glowing clouds to lure in prey attracted to the light, much like moths to a flame. The prey is easily captured and ready for the shark to feast on.
9. The Anglerfish’s Luminous Fishing Pole
The anglerfish, with around 200 species, resides in the dark, deep oceans—so deep that sunlight never reaches. But that’s no problem for the anglerfish; it generates its own light.
Female anglerfish have a section of their dorsal spine protruding from their heads like a fishing rod, with a glowing orb at its tip. Like other fishermen, this rod has bait. The light attracts prey, and once close enough, the anglerfish strikes with its huge, crescent-shaped mouth filled with slender, translucent teeth.
The anglerfish's body is so flexible that it can consume prey up to twice its size, which is remarkable considering the largest anglerfish can exceed 1 meter (3 feet) in length.
8. The Hawaiian Bobtail Squid’s Million-Strong Invisibility Army
By day, this bobtail squid stays buried in the sands along the shores of Hawaii. However, at night, it ventures out to hunt while avoiding becoming prey itself, with a little assistance from an unexpected source.
Within the Hawaiian bobtail squid’s mantle is an organ specifically designed to host a culture of bacteria. This isn’t a case of infection, though. In fact, shortly after birth, the squid deliberately attracts these microorganisms using a special mucus to bring them to its body.
The bacteria emit just enough light to mimic the glow of the Moon in the ocean, allowing the Hawaiian bobtail squid to blend in perfectly with its environment. This camouflage keeps it safe from predators while it hunts. In return, the bacteria benefit from the sugars and amino acids the squid provides.
7. The Red Searchlight of the Black Dragonfish
The majority of bioluminescence in the ocean is blue light. This is likely not a coincidence, as blue light is highly visible to most marine creatures and can travel far through the water. In contrast, red light is absorbed quickly by the ocean, and most animals cannot perceive colors like red or yellow.
A remarkable exception is the black dragonfish. It produces a short-wavelength color, similar to blue, which is then filtered through a fluorescent pigment inside its body. This process lengthens the light and turns it red before it is emitted into the ocean. But why go through the trouble when red light doesn’t travel far?
What makes this dragonfish unique is its ability to produce red light and perceive it. Very few marine creatures can do this, giving it a significant advantage when hunting. Its red light allows it to see prey, while the prey remains unaware and blind. The black dragonfish emits light that only it can detect, offering it a major strategic edge in ocean combat.
6. The Lethal Glow of the Bioluminescent Octopus
With tentacles extending up to 36 centimeters (14 inches) from its body, the Stauroteuthis syrtensis, also known as the bioluminescent octopus, captivates with two striking features. The first is a webbing that links its tentacles, giving it a striking umbrella-like shape. The second is the modified suction cups that glow with a dazzling blue-green light.
The exact purpose of this glow remains uncertain, as the octopus resides at depths of up to 4,000 meters (13,100 feet) beneath the ocean's surface. However, its diet is largely composed of small planktonic crustaceans, which possess well-developed, light-sensitive eyes that are drawn to sources of light.
The bioluminescent octopus likely uses its glowing lights, both steady and pulsing, to captivate the crustaceans. Once they are close enough, it deploys a mucous web to trap them and guide them to their doom.
5. The Cookiecutter Shark’s ‘Broken’ Camouflage
The cookiecutter shark uses a strategy akin to that of the Hawaiian bobtail squid, which employs light to blend in with its surroundings and evade predators by matching the light from above. With photophores located primarily on its stomach, the cookiecutter shark employs a technique known as counterillumination to conceal its body from predators that would otherwise easily spot and devour it.
The photophores effectively disguise the cookiecutter’s entire body—except for one noticeable detail. Around its neck is a “collar” that lacks photophores, creating a gap in the shark’s counterillumination. While most of its body remains hidden, this small portion of its neck is left exposed.
At first glance, this might seem like a design flaw, as complete camouflage would seem more effective. But that gap in the shark's camouflage actually transforms its defensive tactic into an offensive one.
The visible neck portion acts as bait, luring in would-be predators who think they’re attacking a smaller fish. However, these predators are unprepared for the larger, much more dangerous creature they are about to engage with.
When the predator attempts to strike the exposed neck, it is met with the cookiecutter’s powerful suction and razor-sharp teeth. Once the shark secures its grip, it spins wildly, ripping a chunk of flesh from its unsuspecting attacker.
4. The Green Bombs Of The Swima Worms
Along the seabed off the West Coast of the United States lives a genus of sea worms known as Swima, designed much like a long rowboat. They possess rows of fan-shaped bristles which they use as paddles to navigate through the ocean depths.
While these bristles give the worms their unique form, the most remarkable feature of the Swima is found in a small cluster near their heads. These small, green-colored gills have earned the Swima its nickname: 'The Green Bombers.'
When threatened or disturbed, the worm detaches one of these green 'bombs' and uses it as a decoy. Once detached, the gill emits an intense green glow to draw attention away from the worm, allowing the Swima to escape the danger. On average, each worm is equipped with about eight of these glowing bombs at any time.
3. The Fire-Spitting Shrimp
Acanthephyra purpurea is a species of shrimp that lacks any bioluminescence. In fact, it might appear like a typical shrimp. On a quiet day, it wouldn't catch anyone's eye. It has no photophores, and its body doesn't produce any light.
However, this shrimp has a unique biological ability to generate and store a chemical compound known as luciferin. If it faces danger, it ejects this compound in a manner that might look like vomiting to an observer.
When the luciferin comes into contact with the oxygen in seawater, a chemical reaction occurs that produces a glowing effect. This bright display resembles blue flames, providing the shrimp with a chance to create a distraction and quickly escape, ensuring it can 'spit fire' again if needed.
2. The Milky Glow Of The Hitchhiker Bacteria
In 1995, the SS Lima, a British merchant vessel, sailed through a patch of ocean that radiated a milky white glow. For six hours, the ship drifted through what the captain described as a scene akin to snow or clouds.
This glowing stretch of ocean might have seemed like something out of a fairy tale, but it was the result of an immense colony of bioluminescent bacteria. These glowing microorganisms drift freely in the ocean, though not typically in such large clusters as those encountered by the Lima.
However, glowing requires energy, and no living organism wants to expend its resources unnecessarily. The light emitted by these bacteria actually serves a purpose: it's a form of invitation. While many creatures use bioluminescence to avoid being preyed upon, these bacteria employ it for the opposite reason.
The glow acts as a signal to fish and squid, enticing them to feast on the bacteria. After all, a fish's stomach is rich in nutrients, and the fish can carry the bacteria much farther than they could drift on their own.
1. The Squid Willing To Make Sacrifices
The Octopoteuthis deletron is a squid that dwells in the frigid depths of the Pacific Ocean, taking the strategy of the green bomber to an extreme level. To defend itself from its many predators, this squid is ready to make significant sacrifices in order to survive.
When faced with a life-threatening predator, the squid grabs onto its attacker with its limbs, then deliberately detaches those limbs. While the squid tries to escape, its discarded tentacles continue to flail and emit light, distracting the predator long enough for the squid to slip away.
This is a perilous gamble, as regenerating lost limbs demands energy, which will be harder to acquire while swimming and feeding with missing appendages. But as cephalopod researcher Stephanie Bush remarked, 'The cost is less than being dead.'
