Most of the aliens that come out of Hollywood don’t really look alien at all. They may have pizza-size eyes or roachlike antennae, but their oddities are draped on a familiar humanoid frame.

If you want to find life forms that truly seem otherworldly, your local forest is a much better place than your local cineplex. It is home to creatures that are immensely old, fundamentally bizarre and capable of startlingly sophisticated behavior. They are the slime molds.

Slime molds are a remarkable lineage of amoebas that live in soil. While they spend part of their life as ordinary single-celled creatures, they sometimes grow into truly alien forms. Some species gather by the thousands to form multicellular bodies that can crawl. Others develop into gigantic, pulsating networks of protoplasm.

While naturalists have known of slime molds for centuries, only now are scientists really starting to understand them. Lab experiments are revealing the complex choreography of signals in some species that allows 20,000 individuals to form a single sluglike body.