Urban legend says that when Earth is entirely devoid of life, cockroaches will be the one species to survive us all, and scientists may have discovered why — partially, at least. In a morbidly fascinating study published in Proceedings of the Royal Society B, scientists at Université libre de Bruxelles have found that cockroaches have unique personalities.

Plenty of animals besides humans have this trait, including dogs, cats, and sharks. Studies have shown that certain invertebrates too have distinct personalities, and the researchers wanted to see if that included roaches. Indeed, it does. The trait, scientists say, may help explain why the seemingly ubiquitous pest is so good at surviving.

The group attached transmitters to “19 groups of cockroaches with 16 individual same-age males in each,” reports Phys.org. Three times a week, they let each group was let loose in an enclosed, dark plastic arena. Phys.org explains:

Just above the arena, the team placed several disks that would cast shadows down below when the lights were turned on. This allowed the researchers to track the roaches as they sought to hide in the shadows, or not, both individually, and when they were members of a group.

In analyzing the behavior of the cockroaches, the researchers found that there were clear differences in personality between individuals—when left alone, some would scurry to hide as soon as the light was turned on, while others dawdled or ignored the light altogether. They also found that some took a lot longer to work up the nerve to venture out after the light remained on for a long period of time. The researchers also found that the individual personalities tended to result in a group personality that was evidenced by how long it took a group as a whole to hide in the shade after the lights came on or how long it took to disperse. Notably, they also found that the behavior of the individual roaches was different depending on if they were alone or in a group—running to hide, for example when with a group when they would not do so when alone.

Acting autonomously above a herd mentality, the researchers say, helps a species survive because it enables creatures to choose new paths and spread into different areas. As for why they’ll outlast humans? Well, that’s a myth, but it’s true that they’re likely to survive a nuclear war.

(Photo: Jeremy Page)