Sunday, 22 May 2011

A resourceful bumblebee

Iris flowers are tricky for bees. They are quite unlike other flowers. Basically, each flower is made of a wide landing platform with striking nectar guides, but to be able to collect the nectar, bees have to push through a lip pressing against this platform - on top of this lip are first the stigma and then the anthers. As the bee enters, it often looks like it has to press with some force to lift the lip to form a gullet high enough. As she enters, its back presses against the stigma, depositing any pollen it might carry; then her back rubs against the flower's anthers, collecting some pollen. On her way back, the bee presses the stigma against a groove, so preventing self-fertilisation. This contraption ensures that visited flowers get cross-pollinated. Long-tongued bumblebees, Bombus hortorum and B. pascuorum and fork-tailed flower bees, Anthophora furcata, are able to enter the flower and feed the way the flower intended. Today I saw a buff-tailed bumblebee, Bombus terrestris, landing on the flowers of Iris versicolor, and appearing to have sensed there was nectar in them, tried in various ways to enter a flower, failing. The bumblebee started then biting the flower lip, in an unsuccessful attempt to gain entrance (top, check its jaws wide open). In other posts I have dealt with this piercing technique used to successfully steal nectar from tubular flowers like comfrey and honeysuckle, where this short-tongued bumblebee cannot reach the nectar.
Not this way - it missed the entrance and got on top of the lid
not this way either...
... and probing with its tongue for nectar after biting the flower lip.
Although this bumblebee was unsuccessful this time, the persistence of its behaviour after failing to get nectar first time round attests to the resourceful behaviour of this successful bumblebee.

1 comment:

Phil said...

Fascinating. Bumblebees seem to be particularly good at stealing nectar from broad beans by chewing a hole in the corolla tube and occasionally I've seen them bite their way into Aquilegia nectar spurs. I've got yellow flag iris in my bog garden and only big bumblebees are strong enough to force their way in - when they flower I'll watch and see if the bumblebees behave like yours....