Starving honeybees lose self-control.

Impulsivity, the widespread preference for a smaller and more immediate reward over a larger and more delayed reward, is known to vary across species, and the metabolic and social hypotheses present contrasting explanations for this variation. However, this presents a paradox for an animal such as the honeybee, which is highly social, yet has a high metabolic rate. We test between these two competing hypotheses by investigating the effect of hunger on impulsivity in bees isolated from their social environment. Using an olfactory conditioning assay, we trained individuals to associate a small and a large reward with or without a delay, and we tested their choice between the two rewards at different levels of starvation. We found an increase in impulsive behaviour and an associated increase in dopamine levels in the brain with increasing starvation. These results suggest that the energetic state of an individual, even in a eusocial group, is a critical driver of impulsivity, and that the social harmony of a group can be threatened when the energetic states of the group members are in conflict.