Roly-poly bugs, pill bugs, woodlice – whatever you call them, it seems these terrestrial crustaceans may have more charisma up their sleeves than their comical tendency to morph into a living ball. A growing body of research has found that pillbugs may be a candidate for personality, as aspects of their behavior have been shown experimentally not able to be explained away by selection, size, or sex. Could it be that fortune favors the bold pillbug?
The species of pillbug studied in a recent paper were Armadillidium vulgare, a widespread non-insect arthropod that’s keen on loitering under rocks and logs – which is probably why most of Europe knows them as woodlice. A. vulgare has also been spotted feeding on human corpses, so make of that what you will. They’re nocturnal and largely stick to sheltered habitats, which is what makes them good models for observing boldness.
Researchers put 100 pillbugs to the test in 24 trials, held across time and contexts to remove the factors of age and location when studying their predictability. They were looking to see how long it took pillbugs to emerge from a hiding place in a synthetic habitat after being disturbed. Essentially, they were looking to see if some pillbugs were more adventurous than others.
Their results showed significant differences between individuals, with different pillbugs being bolder and more predictable than others. The repeated trials also showed that each individual’s behavior type was pretty consistent.
A pillbug’s predictability didn’t seem to infer how bold it was likely to be, which the researchers say indicates that selection is unlikely to play a role for the traits assessed in their study. That means that evolution alone can’t account for the likelihood of a pillbug being bold or predictable, as if it were, you would probably see correlated traits rather than random pairings of bravery and predictability.
Their results also revealed that these traits weren’t associated with a particular size or sex among pillbugs, and that the availability of food didn’t alter their behavior. If these life histories and alluring treats don’t influence a pillbug’s boldness then what can account for the significant differences between individuals? Previous research has suggested that it could be personality.
It’s difficult to imagine something so small and seemingly elusive as a pillbug having a personality, but the authors of “Roll with the fear: environment and state dependence of pillbug personalities” not only posited that it might be possible, but also that pillbugs would be a good model for studying personality.
“Here, we demonstrated substantial differences in risk-taking of A. vulgare,” they concluded about their 2019 study. “Our results suggest that among-individual variation, behavioural plasticity and residual variation are all biologically relevant components of an individual’s behavioural strategy.”
“We recommend studying behavioural variation in an integrative approach and along longer observational periods, as animal personality sensu lato, or in other words, individual behavioural strategy seems to be indeed more than just variation in mean behaviour. […] We propose pill bugs as promising models for personality research due to the relative ease of getting repeated behavioural measurements.”
With research into animal sentience enlisting more and more species in recent years, it could be time to readjust the way we think about pillbugs and treat these curious critters accordingly. After all, do you really want to have beef with an army of armored balls?
The 2023 paper was published in Animal Behaviour.