Do arthropods feel anxious during molts?

The molting process of arthropods, chiefly controlled by ecdysteroids, is generally considered very stressful. Our previous investigations have shown that crayfish, after having experienced stressing situations, display anxiety-like behavior (ALB), characterized by aversion to light in a dark/light plus-maze (DLPM). In the present experiments, the spontaneous exploratory behavior of isolated crayfish was analyzed in a DLPM at different stages of their molt cycle. All tested animals displayed transitory aversion to light similar to ALB, before and, mostly, after molting, but not during intermolt. Injection of ecdysteroids into intermolt animals elicited ALB after a delay of 4 days, suggesting a long-term, possibly indirect, hormonal effect. Importantly, ecdysteroid-induced ALB was suppressed by the injection of an anxiolytic benzodiazepine. Thus, molts and their hormonal control impose internal stress on crayfish, leading to aversion behavior that has the main characteristics of anxiety. These observations are possibly generalizable to many other arthropods.