Beyond the surface: why animals build complex underground cities to survive and thrive

Nature · Published 3 October 2026 Swipe more like this →

In short: A burrow is far more than a simple hole in the ground. From polar bears in snow to clams in rock, animals across nearly every biome engineer these subterranean spaces. Whether for protection from predators, climate control, or food storage, these hidden structures are essential survival tools for countless species.

Burrows are defined as tunnels or chambers excavated into a substrate for habitation, refuge, or as a byproduct of movement. While some are simple tubes, others reach immense complexity, such as rabbit warrens or the vast, interconnected networks of great gerbils. These structures are so extensive that they can be identified via satellite imagery, with occupied burrows often appearing in distinct clusters across the landscape.

Animals are categorized by their relationship to these structures: primary excavators, secondary modifiers, and simple occupants. Primary excavators, like prairie dogs, aardvarks, and wombats, possess the strength to build from scratch. Secondary modifiers, such as pygmy gerbils, adapt existing tunnels to suit their needs, while simple occupants—or commensals—simply move into abandoned spaces. For instance, certain birds utilize burrows originally dug by tortoises, highlighting the ecological interconnectedness fostered by these structures.

The benefits of burrowing are profound. Underground, animals find a stable microclimate that offers insulation against extreme temperatures, protection from fire, and a safe environment for raising young. Some species, like the Adelaide pygmy blue-tongue skink, even use their burrows as defensive strongholds during territorial fights. Beyond living animals, these structures leave a lasting legacy; they are frequently preserved in the fossil record as trace fossils, providing scientists with a window into the behaviors of ancient life.

Invertebrates also master this craft, utilizing mucus to stabilize sediment and prevent collapse. Whether they are insects, spiders, or sea urchins, these creatures demonstrate that burrowing is a universal strategy for life. From the skin-burrowing scabies mite to the rock-boring clam, the ability to manipulate one's environment remains one of nature's most effective survival mechanisms.

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