https://www.atlasobscura.com/articles/cannibal-ants-soviet-nuclear-bunker
Somewhere near Międzyrzecz in western Poland, there is an abandoned Soviet nuclear installation. Patches of pine and spruce, which had been planted as camouflage, are still doing their job. Vegetation entirely envelopes the concrete entrance, which is blocked off but accessible to bats and determined, rule-breaking humans. On top of a ventilation pipe that juts out from the mostly underground facility, there is big, mound-like nest of wood ants. It is a perfectly normal place for wood ants to live. They feast on the sweet honeydew secreted by aphids dwelling in nearby pine trees, and soak up the rays of post-Soviet sun.
But within the bunker, in a small room at the bottom of that shaft, there was a second colony of ants. These ants had no sun, no warmth, no light, and no honeydew. So they survived on the flesh of their fellow ants.
[...]
To understand the bizarre nature of this colony, one must understand the layout of the bunker. Somewhere inside its reinforced concrete walls, which are over three feet thick, there is a small, closet-like room, cryptically numbered 12. The aesthetic of its walls screams “abandoned Soviet nuclear bunker,” with peeling paint and swelling limewash. The floor, once terra-cotta, is now a pile of rubble and soil. In the ceiling is a hole that holds the ventilation pipe, which is approximately a foot wide and connects the chamber to the outside world, about 16 feet above. Ant Colony One, which rejoices in the light and imbibes sweet honeydew, lives right on top of the pipe’s opening. “These ants are mostly eating aphid [honeydew],” Maák says. But when an unlucky ant takes one wrong step, it can tumble down the perilous chute, where it becomes a member of Ant Colony Two. No light, no aphids, no escape. “These ants are eating corpses,” he says.
Ant Colony Two’s drive to survive resulted in an extraordinarily meticulous ant necropolis that lined the walls of the small room and spilled through the doorway. “They were organizing their corpses in waste piles, putting neatly in the corners, and transporting it away,” Maák says. There were approximately two million corpses, many of which displayed bores from bites and fret holes—signs that their contents had been consumed, he says.
