Ants can build a bridge out of their own bodies

Army ants and some fire ant species, when they hit a gap in the terrain — a crevice, a stream, a break in the leaf litter — will lock their bodies together into a literal bridge that the rest of the colony walks across.

The ants at the edge of the "bridge" seem to judge on their own whether it's worth stretching the structure further or cutting the route short at the cost of their own effort — the colony as a whole behaves as if it's optimizing the path, even though no single ant knows the overall plan.

Fire ants take it a step further: when flooded, they link legs and jaws into a floating raft that keeps the entire colony — queen and larvae included — afloat on the water's surface for weeks.

It sounds made up, but it's well-documented behavior: a single ant is basically mindless, yet thousands of ants together form a structure that behaves almost like a piece of engineering.