How does a jellyfish sting people?

Answer 1

Each jellyfish tentacle is covered with thousands of cells called cnidoblasts, which house nematocysts containing stinging threads. When a jellyfish encounters another object, pressure inside the nematocyst causes the threads to uncoil. The stinging cells spring out at the unwitting victim like tiny darts, firing venom into it. The venom is a neurotoxin designed to paralyze jellyfish prey. Although a jellyfish can kill a small aquatic animal, its sting is not usually fatal to humans. It tends to cause pain, skin rashes, fever and muscle cramps. The degree of pain and reaction to a jellyfish sting can depend on the species -- larger jellyfish have larger cnidoblasts that can penetrate deeper into the skin, and some jellyfish have stronger venom than others.