Planarians are small, flatworms from the group Platyhelminthes, found mostly in freshwater environments. Despite being simple animals without a skeleton, they possess an astonishing ability that fascinates both laypeople and scientists alike: extraordinary regeneration.

In one scientific experiment, researchers cut a single planarian into 279 pieces, and each piece regenerated into a fully functional, living worm! This means that one worm can produce nearly 300 genetically identical copies of itself—without fertilization or special lab assistance.

How is this possible?
Planarians contain special stem cells in their bodies called neoblasts, which make up around 20–30% of all their cells. These cells have the remarkable ability to develop into any type of tissue—from muscles and nerves to eyes and intestines. When a planarian is cut, these neoblasts become activated, move to the wound edge, and begin regenerating the missing parts.

How long does regeneration take?
Regenerating a head, including eyes and brain, can take 5–10 days, depending on the worm’s size and the water temperature. Within a few weeks, the planarian can become fully functional again.

Because of this unique trait, planarians are widely used in research on stem cells, tissue regeneration, and even aging. Scientists hope that one day, the knowledge gained from these creatures can be applied to treating injuries in humans.