Decision making in honeybees: a time to live, a time to die?

Abstract

Honeybees that sting vertebrate predators embed and leave their stingers in the flesh of the stung animal and die shortly thereafter. To determine whether bees make life-or-death decisions based upon risk–benefit evaluations, the vigor of defenses of colonies that had a small loss potential versus those that have large loss potential was compared. Colonies 3–4 days old have small reserves, and thus, risk fewer reserves to lose to a potential predator. In contrast, colonies 19–22 days old risk large quantities of vulnerable immature brood, constructed wax comb, nectar/honey, and pollen and have limited future reproductive potential if their nest is abandoned. As predicted by a risk–benefit hypothesis, older colonies with much at risk sent proportionately larger percentages of stinging defenders to confront threats than younger colonies with less to lose. The percentage of defenders that issue from the 19–22-day-old colonies correlated with the population of workers within the colonies. The percentage of workers that attack strongly increased as the weight of colony-fixed resources within the combs increased. In queenless colonies having no potential to reproduce by swarming and little, or no, reserves of nectar or pollen, only a small percentage of workers defended the colony. These results provide support for the ability of defending honeybee workers to make life-or-death decisions based on evaluating risks of colony loss versus the benefit derived from their personal loss of life.