The animal kingdom is wonderful. It features millions of different species of living forms that are so unlike to one another that they appear to be from separate worlds. The fearsome Bengal tigers that chase their prey in jungle regions have little in common with sea mollusks that crawl from the depths of the ocean floor and change their texture and color to hide from predators.

The diversity of Earth’s organisms is indeed astonishing. Many of them have unexpected, curious, and incredible characteristics. For example, two recently documented species of slugs are capable of surviving a self-inflicted decapitation, and after two weeks their bodies grow back.

The escape artist

We know that many species of reptiles, arthropods, rodents, and amphibians, among others, are capable of detaching themselves from a part of their body, such as a limb, their skin, or one of their organs, to free themselves from a predator’s attack. The lost limb then grows back.

This survival mechanism has been observed and studied in detail for decades. The process by which an animal can recover an amputated part of its body is called autonomy or autoamputation. Regeneration is not always effective and takes considerable time when the animal is most vulnerable and exposed to danger. Even so, it is not the resource most chosen by animals, but rather they adopt it in extreme conditions.

But not all self-mutilation processes in the animal kingdom are linked to self-defense. A team of researchers from the University of Hiroshima found that two species of sea slugs mutilate their heads. Once decapitated, they continue to live completely normally until their body regenerates after about 17 days.

But they don’t do this to escape a predator. The researchers stimulated the slugs, imitating predatory behavior, but that did not cause them to self-mutilate. The factors that could have caused the self-mutilation are still not entirely clear to the experts, but they assure that it has nothing to do with surviving an attack because the mollusks take several days to completely detach themselves from their bodies, which is not desirable in an emergency.

In their study published in Current Biology, the authors suggest that it is a mechanism to get rid of a parasitic infection.

The headless slug

The experts monitored the evolution of a bunch of slug specimens and found that under certain conditions, the animals shed their bodies, ridding themselves of all their organs, including their hearts. After a few hours, the wound on the neck was closed. On the eighth day, they had generated a new heart and just two weeks later, their entire body had regenerated.

More than half of the slugs successfully survived self-mutilation. The rest—coinciding with the older population—survived no more than 10 days. Incredibly, even without a digestive system or even a heart, slugs are capable of feeding on algae during their recovery process.

“The reason why the head can survive without the heart and other important organs is not clear. We have achieved complete rearing of (these slugs) for multiple generations; therefore, they can be used as a model system to study autotomy and the regeneration of the body,” the authors say in their research.

They then add: “It is not clear why these slugs can regenerate their body even if they lose most of their organs, but we suspect that it is a kleptoplasty. In (one of the species studied) a highly branched digestive gland extends over most of its body surface, including the head, and the gland is lined by cells that hold the chloroplasts of ingested algae. Thus, these slugs can obtain energy for their survival and regeneration from kleptoplast photosynthesis, even when they can’t digest food,” which would explain how slug heads survive decapitation in the first place.

Have we found the secret to regenerating human organs?

For many experts, this field is the Holy Grail of knowledge, as future research could allow us to understand and reproduce the amazing mechanisms of cell regeneration that we observe in the animal kingdom. This could allow us to apply it in innovative clinical technologies that promote soft tissue regeneration in the human body, for example.

“Someday, patients will have access to regenerative medicine treatments that will circumvent the complications of organ donation. […] Instead of transplanting organs, we will know how to repair our own,” Sharlini Sankaran, executive director of Duke University’s Regeneration Next Initiative, told Big Think.