Why do grasshoppers jump so high?

Answer: Their hind legs store energy like a coiled spring

Their hind legs store energy like a coiled spring ✓ — Correct! Before a jump, the big muscle in each hind leg squeezes slowly for a fraction of a second while a catch holds the knee shut, bending stiff, springy parts of the joint like a drawn bow. When the catch lets go, that stored energy snaps the leg straight far faster than muscle alone could move it. A locust can clear about twenty times its body length this way.

Their bodies are so light that they float upward — Wrong. A light body helps a little, but it does not lift anything by itself. Grasshoppers cannot float; every jump is powered by energy their legs stored in advance, and a heavier locust jumps just as impressively for its size.

They ride rising air currents to gain height — Wrong. Grasshoppers jump just as well in still air, so moving air is not the source of the height. The power comes from the catapult mechanism in their own legs, released in a few thousandths of a second.