Lazy bumblebees are not defensive reserves

Bumblebees sting, but that is not the only reaction they can have when their nest is disturbed. Here we examine the behavior of those individuals that remain inside the nest during a disturbance. We explore the hypothesis that inactive individuals are ‘defensive reserves’ and therefore more likely to respond when the colony is disturbed. We administered CO2, vibration, and pure air into two colonies on alternating days and measured the movement and task performed by a random subset of bees inside the nest. Our results show that individuals that remain inside the nest increase their activity during and after a vibration disturbance, and that regardless of the disturbance type, individuals are most likely to increase perching behavior (i.e. a stationary guarding posture) after a disturbance stops. With regards to the defensive reserves hypothesis, there is no evidence to suggest that, in bumble bees, inactive individuals are more likely than other nestmates to respond to a disturbance, and should therefore not be considered defensive reserves. We conclude that although the spatial organization is disrupted during a disturbance, there is evidence that individuals can quickly return to their pre-disturbance behaviors after a disturbance has ended.