Stop thief! This bumblebee is engaged in the act of "nectar robbing". I mentioned last week that the Comfrey on the allotment attracts the biggest, fattest bumblebees. Their tongues are long enough to reach right into the flowers for the nectar they crave (thereby facilitating pollination as they feed on the nectar).
 The smaller bees aren't able to do this but get around the problem by piercing a hole closer to the stem and drinking from it or taking advantage of a hole that has already been opened. However this bypasses the flower's reproductive structures and I noticed that even the big bumblebees were sometimes nectar robbing from open holes- an easy fix I suppose.