Leeches Have 32 Brains

The source of the "32 brains" claim lies in the leech's segmented body. Its nervous system is uniquely decentralized; each of its 32 segments contains its own ganglion, a dense cluster of nerve cells. While not a brain in the human sense, each ganglion acts as an independent processing center, coordinating the movement and sensory input for its specific section. This distributed network (Review) allows for the leech's signature inching locomotion and gives it remarkable regenerative capabilities. Two larger ganglia at the head and tail serve as more complex control centers, but the overall system is a marvel of distributed biological computing.

This intricate anatomy is perfectly engineered for a blood-feeding lifestyle, a fact that has placed leeches in medical history for centuries. A leech uses three sharp jaws, each lined with around 100 tiny teeth, to create a distinct Y-shaped incision. Its saliva contains both an anesthetic to numb the host and a powerful anticoagulant, hirudin, to ensure a steady flow of blood. To make the most of a rare meal, a leech can store up to ten times its body weight in blood within its 10 stomach sacs, a feast managed by two separate hearts. This unique combination made them central to