Bumblebee grooming

Moss carder bumblebee (Bombus muscorum (Linnaeus,1758) on bell heather with pollen grains. Spain (28/08/2016)

Looking at this photograph of a bumblebee with a sprinkling of pollen grains on its head, made me wonder, how often do they groom themselves? Some bumblebees get absolutely covered in pollen! Here’s one grooming himself on the flower-head of an aster (below).

White-tailed bumblebee (Bombus lucorum) grooming the pollen off its legs and body

Bumblebees often groom themselves whilst flying between flowers – talk about multi-tasking! – especially when they are actively collecting pollen rather than just nectaring (feeding on nectar). Photographing bees grooming in flight is not easy, but there are some good videos of bumblebees grooming themselves, which people have posted on the Net (see Links 1 and 2).

Early bumblebee (Bombus pratorum) in flight, with small yellow pollen basket

Both bumblebees and honey bees, (Apis mellifera) groom themselves very frequently and collect the pollen grains in their corbiculae (or pollen baskets). Well-groomed bees are however, not very useful to the plants they feed on, because once the pollen grains are stored in the baskets on their back legs, they are not available for pollination. Pollen which remains on the bodies of the bumblebees, is available to be transferred to the next few flowers that are visited. A few grains remain attached to the bee for some time and in this way travel much further as the bee moves from one clump of flowers to the next. Of all the pollen shed by a flower and picked up on the hairs of a bumblebee, only a very small proportion – less than 1% – actually reaches the stigmas of other flowers and does the job that it was produced for. Nevertheless, it is one percent of a very large number and is clearly enough to do the job of pollination, even though the bees take – or waste (!), as some of it just falls off – a very high proportion of the available pollen!

White-tailed bumblebee (Bombus lucorum) with a very full pollen basket

Bumblebees groom themselves efficiently and redistribute the pollen on their bodies, either storing it in pollen baskets (above) or – presumably in the case of males and cuckoo bumblebees, which lack pollen baskets – discarding it? N.B. only ‘true’ bumblebee workers and queens collect pollen. Researchers have discovered that the more pollen a bumblebee accumulates on its body, the more likely it is to start grooming. That’s supposing it does not fancy a snooze first! This queen Red tailed bumblebee (below) I photographed on 11th April this year (2017) in Bedfordshire seemed more intent on dozing in the Spring sunshine – or was it looking for a nest site? – than grooming itself!

A Red tailed bumblebee queen (Bombus lapidarius), having a rest in April sunshine

So it may be that bumblebees are prepared to tolerate a slight smattering of pollen without feeling the need to groom themselves? It is certainly in the plants interests that they do not keep their bodies completely free of pollen. There may also be a balance to be had between spending time on nectaring and spending time grooming. Although, if they can do their grooming on the wing, between flower visitations, they save themselves a lot more time for feeding. Remarkably, some plants – such as Lupinus (lupin) flowers – control the amount of pollen that can be removed during a single visit by a bee; presumably to avoid having it all scooped up into pollen baskets! Pollen collected in this way is effectively ‘lost’ as far as the plant is concerned because it will never reach a stigma and fertilise another flower.

White-tailed bumblebee (Bombus lucorum) getting heavily dusted with pollen on an aster

The length of time a bumble-bee spends at a given flower, depends on the amount of nectar available; rather than the amount of pollen. Bees are not the only insects to get covered in pollen of course. I came across some invasive Asian hornets feeding (or gathering pollen?) in among the heather in Spain, and they were heavily dusted with pollen (below). How efficient they are at grooming, and what they do with it, I have no idea (feed it to their offspring perhaps?).

The Asian hornet (Vespa velutina) covered in pollen whilst feeding in heather. Galicia, Spain

I will finish with a picture of a very well-groomed bee! I photographed this White-tailed Bumble Bee (Bombus lucorum) worker (below) in Yorkshire on 18th July this year (2017); it appears to have an empty pollen basket (the shiny hairless patch on the tibia of the hind leg). Perhaps it was newly emerged and had only just started foraging?

White-tailed Bumble Bee (Bombus lucorum) worker with empty pollen basket highlighted

Links to bumblebess grooming

  1. https://www.youtube.com/watch?v=-91iFabsHrQ
  2. https://www.youtube.com/watch?v=Ex5HOS4IkEc

References associated with grooming and pollen transfer

Castellanos, M. C., Wilson, P., & Thomson, J. D. (2003). Pollen transfer by hummingbirds and bumblebees, and the divergence of pollination modes in Penstemon. Evolution57(12), 2742-2752.

Cresswell, J. E. (1999). The influence of nectar and pollen availability on pollen transfer by individual flowers of oil‐seed rape (Brassica napus) when pollinated by bumblebees (Bombus lapidarius). Journal of Ecology87(4), 670-677.

Harder, L. D. (1990). Behavioral responses by bumble bees to variation in pollen availability. Oecologia85(1), 41-47.

Harder, L. D., & Thomson, J. D. (1989). Evolutionary options for maximizing pollen dispersal of animal-pollinated plants. The American Naturalist133(3), 323-344.

Rademaker, M. C. J., De Jong, T. J., & Klinkhamer, P. G. L. (1997). Pollen dynamics of bumble‐bee visitation on Echium vulgareFunctional Ecology11(5), 554-563.

Thomson, J. D. (1986). Pollen transport and deposition by bumble bees in Erythronium: influences of floral nectar and bee grooming. The Journal of Ecology, 329-341.

Thomson, J. D., & Goodell, K. (2001). Pollen removal and deposition by honeybee and bumblebee visitors to apple and almond flowers. Journal of Applied Ecology38(5), 1032-1044.

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