A massive colony of up to one million “cannibal ants” that have been trapped in a nuclear bunker in Russia for years have escaped, scientists in Poland say.

Newsweek reports that the ants, first discovered in 2013, are now running free.

“In a study published in the Journal of Hymenoptera Research, researchers have now studied the colony to understand how it functioned—and installed an escape route to see if its members would leave their home given the option,” Newsweek wrote.

The team, led by Wojciech Czechowski, from the Museum and Institute of Zoology and the Polish Academy of Sciences, were carrying out a survey of bats living in an abandoned Soviet nuclear bunker when they came across the wood ants living in an ammunition bunker where nuclear weapons were once kept. The ants had no access to the outside world and appeared to have come from a nest above that was positioned over a ventilation pipe. When the ants fell down the pipe, they were entombed in the bunker. TRENDING: HERE SHE COMES! Judge Amy Coney Barrett Seen Leaving Her House with Her Seven Kids and Husband! -- Announcement at 5 PM ET However, after returning to the site two years later, scientists found the colony was not only still there, but that it had grown in numbers. This was despite there being no obvious food source, no heat and no light. A population estimate suggested there were hundreds of thousands, if not one million ants living in the bunker.

The ants are known as Formica polyctena. “Formica polyctena is a species of European red wood ant in the genus Formica and large family Formicidae. The species was first described by Arnold Förster in 1850,” says its Wikipedia entry. “It is found in many European countries. It is a eusocial species, that has a distinct caste system of sterile workers and a very small reproductive caste. The ants have a genetic based cue that allow them to identify which other ants are members of their nest and which are foreign individuals. When facing these types of foreign invaders the F. polyctena has a system to activate an alarm. It can release pheromones which can trigger an alarm response in other nearby ants.”

The ants in the bunker had no known food source, which led scientists to believe that they survived for years by cannibalizing the fallen members of their colony.

“Summing up, the ecological and behavioural flexibility of the wood ants … may allow them survival even in unexpectedly suboptimal conditions,” the researchers wrote in a paper. “The survival and growth of the bunker ‘colony’ through the years, without producing own offspring, was possible owing to continuous supply of new workers from the upper nest … and accumulation of nestmate corpses. The corpses served as an inexhaustible source of food which substantially allowed survival of the ants trapped down in otherwise extremely unfavourable conditions.”