If you've ever encountered a cockroach—in your apartment, say, right before you squash it with a shoe—you probably didn't consider whether or not the insects have individual personalities. But researchers at Université libre de Bruxelles did. In fact, they wanted to know if these potential personalities were affecting the collective decision-making of groups of cockroaches.
Nineteen groups of cockroaches with 16 individual same-age males were fitted with tiny transmitters that precisely tracked their movements. Three times a week, each set of cockroaches—both individually and as a group—was released into a dark plastic arena. Lights were flicked on, and the researchers measured how quickly, if at all, certain cockroaches rushed to the shadowy areas provided.
They found that different cockroaches behaved differently, both from one another and depending on whether or not they were in a group setting. While some immediately hid in the shadows, others seemed to barely notice the bright light suddenly illuminating them. The researchers concluded that this indicated a range of personalities specific to individual cockroaches, and that this diversity of personalities is what makes cockroaches so able to adapt to different situations and surroundings.
Personally, I think it would have been more remarkable if the researchers found that every single cockroach always behaved exactly the same way as every other cockroach, and I'm reluctant to call their findings evidence of a "personality." But next time you start trash-talking cockroaches, consider that the one you're bashing could be a particularly sensitive guy.