By Richa Malhotra
Keep calm and carry on building. That’s the motto of 100,000 or so wood ants stranded without food in a nuclear bunker until they starve.
Wood ants (Formica polyctena) typically build a cosy mound nest on the forest floor. They seek out the sugary secretions of aphids living on trees and supplement their diet with insects. Now, scientists have uncovered a population of wood ants that has sustained for years without food and light inside a bunker where temperatures are constantly low.
The ant population was discovered in 2013 by a group of volunteers counting bats overwintering in the bunker, which is part of an abandoned Soviet nuclear base near Templewo in western Poland.
Later, Wojciech Czechowski at the Museum and Institute of Zoology in Warsaw, Poland, and his colleagues, entered the bunker to study the ants more closely. They noticed that the wood ants had built a nest on the terracotta floor of the bunker – right below a ventilation pipe. Looking up through the five-metre-long pipe, they realised where the bunker ants come from.
A 60-centimetre-high wood ant nest sits on the forest floor directly on top of the ventilation pipe outlet. But because the metal cap over the ventilation pipe has rusted, ants can fall through from time to time.
It’s a one-way journey for any ant that falls into the bunker. They can scale its 2.3-metre-high walls but Czechowski and his colleagues realised that – for some reason – the ants never walk across the bunker ceiling and so are unable to reach the ventilation pipe to make it back home.
So, how did they respond? “These ants gathered together and did what ants do,” says Terry McGlynn, an entomologist at the California State University Dominguez Hills, who was not involved in the study. “They built a nest and eked out an existence.”
Today that nest covers most of the floor of a chamber that measures three metres by one metre.
Czechowski and his colleagues have looked for evidence of a food source that the bunker ants could use, but haven’t found one yet. Rather, the ants seemed to be doomed to starve to death in pitch-blackness. They found ant corpses carpeting the bunker floor in layers a few centimetres thick and estimated the number of dead ants to be about two million.
Without any food, the individual bunker ants are probably dying at a rate faster than at the surface, the researchers think. But because there is a steady stream of new arrivals falling into the bunker, the colony has grown to a reasonable size.
This explains one of the unusual features of this nest. When the researchers dug into it to look for an ant brood they found none – no larvae, pupae or empty cocoons. The “colony” was queenless and lacked any males. This fits with the idea that it is no ordinary nest, but a strange nest-like structure that the worker population has instinctively built.
“This is kind of fascinating that such a huge non-productive nest could exist on its own, built solely from the ants that got trapped in the bunker,” McGlynn says.
Journal reference: Journal of Hymenoptera Research, DOI: 10.3897/jhr.51.9096