A Map of the US…Made of Slime Mold

One-celled organisms could make our road network more efficient

The “roads” on this agar-gel map of the U.S. may not quite mirror reality, but they could help scientists build more-robust networks in the future.

Physarum polycephalum, a type of slime mold, grows tendrils in search of food and withdraws extraneous arms to focus on the most efficient paths between sources. Although the American map is just an illustrative model made for Popular Science, researchers in the U.K. have used slime mold to create similar replicas of local roads and railways, backed up by computer models. Andy Adamatzky and Jeff Jones, specialists in unconventional computing at the University of the West of England in Bristol, found that, left to its own devices, the slime mold mimicked a good part of the country’s actual road systems. Because slime mold finds the paths that are most resilient to faults or damage, it could be used to make mobile-communication and transportation networks hardier.

The following videos, made by the slime mold team at our request, show computer simulations of how Physarum might behave while traveling across the U.S. The simulations demonstrate how slime mold readjusts as time passes and nutrients deplete and gives hints about our own transportation system (although these particular simulations aren’t statistically accurate and don’t account for the different sizes of cities). By the end of each video, the mold has found the most efficient paths and sticks to them, but as the continuous activity highlights, the resilient creature could always form new networks if needed.

The mold begins in New York City on a map with very concentrated food sources in the cities but few nutrients in the countryside. This encourages the slime mold to form only the most direct paths, skipping the barren lands in between. So good luck getting from New York to Boston; according to this map—and probably some New Yorkers—there’s nothing worth visiting in between.

In this video, the simulated slime mold starts spread evenly throughout the land and then adapts its shape to the food sources. The nutrients in the rural areas get gobbled up, and the cities become the main food hubs. As the many paths recede, Michigan’s Upper Peninsula loses its appeal, and the only hope of crossing the West Coast requires a weekend trip to Salt Lake City.