Problem solving by worker bumblebees Bombus impatiens (Hymenoptera: Apoidea).

During foraging, worker bumblebees are challenged by simple to complex tasks. Our goal was to determine whether bumblebees could successfully accomplish tasks that are more complex than those they would naturally encounter. Once the initial training to successfully manipulate a simple, artificial flower was completed, the bees were either challenged with a series of increasingly difficult tasks or with the most difficult task without the opportunity for prior learning. The first experiment demonstrated that the bees learned to slide or lift caps that prevented their access to the reinforcer sugar solution through a series of tasks with increasing complexity: moving one cap either to the right or to the left, or lifting it up. The second experiment demonstrated that the bees learned to push balls of escalating masses (diameters 1 and 1.27 cm) from the access to the hidden rewarding (sugar syrup) reservoir of artificial flowers. In both experiments, when bees with experience with only the simplest task (i.e. an artificial flower without a barrier to the reinforcer) were presented next with the most complex or difficult task, they failed. Only by proceeding through the series of increasingly difficult tasks were they able to succeed at the most difficult. We also noted idiosyncratic behaviours by individual bees in learning to succeed. Our results can be interpreted within the context of Skinnerian shaping and possibly scaffold learning.