Tadpoles recycle their own tails during metamorphosis, breaking down the tissue into nutrients that fuel the growth of legs, lungs, and a stronger jaw.

This biological recycling process is called programmed cell death, or apoptosis. During the final stages of metamorphosis, the thyroid gland releases a surge of thyroxine, a hormone that triggers lysosomes within tail cells to release digestive enzymes. These enzymes break down the tissue from the inside out, a process that is remarkably efficient and wastes virtually no energy during the transition from aquatic to terrestrial life.White blood cells called macrophages migrate to the tail to consume the cellular debris. The resulting amino acids and lipids are redirected to fuel the frog's developing limbs and respiratory system. This energy recycling is critical because the froglet typically stops eating during metamorphosis while its entire digestive tract undergoes complete restructuring.The frog's circulatory system transforms dramatically during this period as well. The heart evolves from a two-chambered structure (like a fish's heart) to a three-chambered organ, allowing the frog to separate oxygenated and deoxygenated blood—a necessity for breathing air. By the time the tail is fully absorbed, the frog's body is physically equipped for life on land. Research published in developmental biology journals has documented this remarkable coordination between tail resorption and the development of new organs, showing how evolution has optimized this transition for maximum survival.