In the last few years there has been a good deal of research into bumble bee behaviour. These astonishing insects are capable of quite complex learning, far more than was at one time recognised. For example they can learn to roll a wooden ball to a target in order to get a reward of dissolved sugar. An article very recent published reports that they also engage in behaviour that looks like playing; they spontaneously roll the wooden balls around even when no reward is associated.
For more about the research see