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Even Cockroaches Have Personality, Scientists Say

Cockroaches may seem like the ultimate mindless machines of the insect world, but researchers report that they actually show a lot of variation on the personality scale, from bashful to bold. What's more, when cockroaches spend enough time with each other, they tend to flock together. Such are the findings from a study published this week in the Proceedings of the Royal Society B.

The personality analysis took the form of an experiment in which cockroaches (Periplaneta americana) were thrown into an illuminated arena with a couple of dark shelters constructed from plastic discs.

Image: Cockroaches
Cockroaches gather together under a plastic shield to hide from bright light. Isaac Planas Sitja / ULB

Roaches don't like to rest in the presence of bright light, as many urban dwellers know all too well, so the researchers studied how different bugs responded to a sudden glare. Some of the roaches sought shelter quickly during repeated trials, while others were willing to stay out longer. The research team argues that this is a manifestation of cockroach personality.

When groups of 16 roaches were thrown into the arena together, they generally came to a consensus about when and where to seek shelter. But the pattern varied from group to group. "The sheltering dynamics are sensitive to the composition of the group," the researchers reported.

They speculate that there may be advantages to the diversity of cockroach lifestyles, as well as the tendency toward cockroach flocking. "In cockroaches, as observed in other insects, a limited plasticity can be the least costly and evolutionarily most beneficial strategy," they wrote.

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Isaac Planas-Sitja, a behavioral ecologist at the Free University of Brussels, is the principal author of the study, titled "Group Personality During Collective Decision-Making: A Multi-Level Approach." Co-authors include Jean-Louis Deneubourg, Celine Gibon and Gregory Sempo.