Lars Chittka at Queen Mary University of London and his colleagues presented bumblebees (Bombus terrestris) with a disc that had been filled with sugar water and placed under a transparent sheet of Plexiglas. To get at the disc, the bees had to pull on a string attached to it (pictured). Just 2 bees out of almost 300 worked out how to do this on their own; most needed stepwise training, after which more than 80% of bees were successful.