Sea Cucumbers Defend Themselves by Spilling Their Guts—Literally

Sea cucumbers may appear slow and unassuming, but they have developed an incredible and unforgettable defensive strategy. When threatened or attacked, as seen in this Facebook video, sea cucumbers quite literally spill their guts!

All About Sea Cucumber Species

Sea cucumbers are marine invertebrates found in every ocean around the world. There are over 1,700 known species, ranging from less than an inch to over 6 feet long. Although many have elongated, rounded bodies covered in bumps like a cucumber, others display a wide variety of shapes and colors. Sea cucumbers belong to the echinoderm group, which also includes sea urchins and starfish. Like their relatives, sea cucumbers have bodies with five-part symmetry, featuring a mouth at one end and an anus at the other. Sea cucumbers move by using peristalsis, which involves wave-like muscle contractions along their bodies.

How Sea Cucumbers Fight Back

Most sea cucumber species are scavengers and peacefully sift through the ocean floor for tiny bits of algae or other microscopic organic material. They are vital to their ecosystems as they clean up bacteria and algae and turn the sediment. This recycling process makes the ocean floor a much healthier habitat for other sea creatures. While sea cucumbers don’t really bother anyone, many other animals consider them to be a rather tasty snack. Crabs, sharks, and various other fish frequently prey on sea cucumbers. Although their squishy, water-filled bodies may appear defenseless, sea cucumbers have developed some extraordinary ways to protect themselves. Many species use clever camouflage to blend into their surroundings and avoid detection. However, if a predator does spot a sea cucumber, it has a rather unusual backup plan.

As seen in this Facebook video, sea cucumbers eject their internal organs in a process called evisceration. This type of autotomy involves expelling parts of the creature’s gut, intestines, and other internal components through its anus directly at a predator. This can serve as a distraction, but there is more to this strange tactic than just diversion. The intestines of many sea cucumber species are toxic, and even a small bite can make a predator sick. Some sea cucumber species also eject sticky, toxic strands called Cuvierian tubules. These strands are like long, strong pieces of a spider’s web and can trap and entangle predators — especially slower-moving ones — giving the sea cucumber a chance to escape.

How Sea Cucumbers Spill Their Guts

When employing this unique defense, a sea cucumber will quickly turn away from its attacker and sharply contract its body muscles. This intense contraction causes the wall of its cloaca (the posterior opening) to tear, causing the anus to gape open. At this point, key internal structures, such as the intestines and tentacles, quickly soften, and their connections within the body weaken. This allows the sea cucumber to forcefully expel its intestines, along with associated blood vessels and other components, through its anus and directly at its attacker.

Some sea cucumbers also expel hundreds of Cuvierian tubules, which are part of their respiratory system. When threatened, water from the respiratory tree is forced into these tubules, causing them to rapidly expand and elongate up to 20 times their original length. Once expelled, these tubules become sticky and can entangle or immobilize predators, providing the sea cucumber with an opportunity to escape.

Regenerating Lost Organs

Spilling its guts may sound like a painful and potentially fatal ordeal, but for the sea cucumber, it is more of a temporary inconvenience. After eviscerating its internal organs, a sea cucumber cannot eat, but it can survive for several weeks by absorbing nutrients directly through its skin. Fortunately, sea cucumbers can regenerate the organs they have lost. Scientists have observed that in some species, regrowth of internal organs can begin within a few days, but complete regeneration may take several weeks.

Are Sea Cucumbers Dangerous to Humans?

Generally, sea cucumbers do not pose a threat to humans. However, their guts contain a toxic substance called holothurin. This can irritate your skin and, if it gets in your eyes, may cause blindness. Ingesting holothurin can cause irritation or illness. Fortunately, sea cucumbers are not aggressive animals. As long as you leave them alone and respect their space, you will be safe.