Yesterday, as I was trying to photograph bees on some unknown shrub in my garden, I noticed that none of the bees was actually entering the flowers of the shrub; the flowers were too small to accomodate the bees' bodies. Instead, the bees appeared to be drinking nectar from the flowers by biting holes through the outside of the flowers. After a while, I noticed that some of the bees weren't biting new holes, but were revisiting old ones.
Then I vaguely remembered reading about such behaviour somewhere in Darwin's correspondence. A quick search later, and there it was. Darwin had written to the Gardeners' Chronicle magazine to elaborate on earlier observations made by other readers:
Darwin, C. R. to Gardeners' Chronicle, [16 Aug 1841]
Perhaps some of your readers may like to hear a few more particulars about the humble-bees which bore holes in flowers, and thus extract the nectar. This operation has been performed on a large scale in the Zoological Gardens […] I observed some plants of Marvel of Peru, and of Salvia coccinea, with holes in similar positions; […] I first noticed them a week since, when, from the brown colour of their edges, they appeared to have been made some time before. The beds of Stachys and Pentstemon are frequented by numerous humble-bees of many very different kinds; at one moment I saw between twenty and thirty round a bed of the latter flower; they fly very quickly from flower to flower, and always alight with their heads just over the little orifices, into which they most dexterously insert their proboscis, and in the case of the Pentstemon, first into the orifice on one side and then into the other, so that they thus extract the nectar on both sides of the germen. […]—C.