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Some surprising experiments on how living things solve problems, leave memories, and build things together.
Ants, humans, and a moving puzzle
Comparing cooperative geometric puzzle solving in ants versus humansTabea Dreyer et al. · PNAS 122, e2414274121 (2025; first published online in December 2024)
How do you get an awkward object through a narrow opening when everyone is pulling on it? Ants and humans tackle the same geometric puzzle, scaled to their size. Larger ant groups navigate more efficiently than smaller ones. Humans generally perform better, but restricting communication makes their teamwork less effective. The authors connect the ants’ improvement to ordered collective motion that retains a short-lived memory.
The physics: a concrete connection between collective motion, memory, and the geometry of a constrained search.
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A memory written on the ground
Slime mold uses an externalized spatial “memory” to navigate in complex environmentsChris R. Reid, Tanya Latty, Audrey Dussutour, and Madeleine Beekman · PNAS 109, 17490–17494 (2012)
Physarum polycephalum has no nervous system, yet it can use the slime it leaves behind to avoid previously explored ground. The key experiment places a U-shaped obstacle between the organism and a food source. Coating the whole surface in slime masks its own trail and makes navigation much less successful. Its surroundings hold a usable record of where it has been.
The physics: chemical attraction and feedback from a deposited trail connect motion to information stored in the environment.
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A raft made of its passengers
Fire ants self-assemble into waterproof rafts to survive floodsNathan J. Mlot, Craig A. Tovey, and David L. Hu · PNAS 108, 7669–7673 (2011)
A group of fire ants can turn itself into a floating raft by gripping neighboring ants. Their linked bodies trap air and create a surface that repels water more strongly than an individual ant does. The paper also follows ants walking across the growing raft: attachment at its edge helps turn individual trajectories into an expanding structure.
The physics: wetting, buoyancy, and self-assembly meet in a material whose building blocks are alive.
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