Science and sensibility

Wednesday, October 13, 2004

Plight of a bumble bee, Part III

You may remember that the last post in this series lamented the death of a queen bumble bee and promised to show what may have been. So we’ll pick up the story by explaining what will be happening around me as emergent queens get fed and establish a new nest.

Following their first shaky flights new queens will spend somewhere near to a week searching for a warm and dry place to set up their nests. So far today I’ve seen three B. terrestris queens hovering low over the ground, occasionally bobbing up and down or ducking into a likely looking spot. The queens don’t actually do much building, though they may move straw or dried grass clippings into a nest site to provide some insulation. One study in New Zealand showed that half of all nests were built in disused rodent nests, which would appear to be ideal as long as the rodent doesn’t return. One of the bumble bee species introduced to New Zealand nests underground.

Once they have set up a nest the queens will make a reconnaissance flight, looping around in ever increasing circles around the nest to orientate herself with her surroundings. During this flight and several subsequent ones they’ll collect nectar and pollen to feed the brood they are about to produce. They will return to their newly founded nest and build two structures from wax. In the centre of the nest she makes a ‘cell’ similar to the ones that make up their cousin the honey bees’ hives, into this she lays about four, fertilised eggs. At the same time a ‘honey pot’ will be constructed to store extra nectar, to start with the stored nectar will feed the queen on days she can’t forage and will later be used to feed her brood.

While her first brood is developing the queen still needs to go on foraging trips to keep her going. Between these trips she sits on wax cell containing her eggs, flexing her flight muscles to generate heat to speed their development. Within four days the eggs will hatch giving rise to larvae which look like grubs with no discernable legs, eyes, wings or hair. The larvae will use their only discernable organ, a mouth, to eat pollen fed to them by their queen. The pollen will drive their development and after about 14 days the larvae pupate. At this stage they will spin a silk cocoon around themselves in their brood cells within which they will undergo the last stages of development, finally hatching abut 14 days later as worker bumble bees.

The inside of a bumble bee nest

With the first set of workers made the queens will settle in to a life on leisure, laying eggs and being fed by the workers. Importantly all the workers she generates will be female and share 75% relatedness. B. terrestris nests have been known to support thousands of workers, though somewhere near to 100 is more common. The role of individual worker bees is determined by their size, with smaller workers staying to tend to the next generation of larva while larger ones go out to forage for nectar and pollen. In turn size is determined by the amount of food developing larvae are fed, overfed commercial (the bumble bee is an important pollinator) and research nests have produced almost queen sized workers.

The foraging worker bumble bees are the ones you see in your garden during the height of summer. They may not cut the most graceful of figures as they bob and buzz about the place but their flight is quite remarkable. A foraging bumble bee has twice the metabolic rate per unit weight of a hummingbird, beating its wings 200 times a second. These workers will forage in what is described as an “optimal” pattern, carefully balancing the large cost of fuelling their flight with the rewards of the energy rich nectar and pollen given by the flowers they visit. They will only fly a long way to a flower if the predicted reward from that flower makes it worthwhile. Workers often develop preferences for particular flowers as well as the colours and patterns of flowers over the four weeks that mark their life. In turn for their sugary reward the foraging bumble bees pollinate many species of plants; in fact, they were introduced to New Zealand from the UK to pollinate red clover which is an important forage crop for livestock. As well as clover bumble bees pollinate monkshood, alfalfa, foxglove and delphiniums, they are not known to pollinate any native plants.

An worker bumblebee taking nectar from some daisies

At some stage in the nest's life the queen will start to lay eggs that she has not fertilised which - if you remember the last post (you should read the comments too) – will develop into males. It is unclear as to what triggers this production of males by the queen but seasonal cues, levels of food and worker bee to larvae ratio are all hypotheses under investigation. The males will develop in much the same way as the female larvae, emerging from their pupal stage about a month after the egg was laid. Male bees are also called drones, they are slighlty smaller than workers, carry the same patern of stripes and do not contribute to the nest at all, eating from the honey reserves for a few days before they leave the nest altogether. The male has one job and that is to successfully mate with virgin queens from other nests, to meet this end males will lay pheromone traps as was described in the first post. Just after the queen starts making males she will choose a few larvae to develop into next season’s queens and thus the circle that started with reflections on a dead queen will be completed. It's worth noting that some B. terrestris up in New Zealand's sub-tropical north can actually survive the winter and keep on going, growing huge supporting thousands upon thousands of workers during the summer.

Earlier I indulged in a rather purple passage comparing the life cycle of a bumble bee nest with denizens of some doomed planet. They also remind me of some of my father’s wisdom so if you’ll allow me another digression I’ll explain it.

I grew up on a plant nursery specialising in “showy” annuals like pansies and petunias, Dad was always amused by the idea held by many gardeners that perennial plants like roses that survived the winter were somehow more ‘refined’ than the ephemeral flowers he sold. The way he saw it annuals had developed a much more elegant solution to the problem of winter, rather than dieing back ever year they spend all summer saving up to put all their efforts into seeds that will survive the cold weather and grow into new plants carrying their parent genes into a new season. I find the idea of hibernating queens lying like seeds under the soil waiting for the warm touch of spring to set off the events that will ensure another summer will be filled with the bumble bee’s buzzing baritone extraordinarily beautiful.

That ends this series of posts but I thought I should point out a few references to works that have proved invaluable in my investigation of the world of bumble bees. In order to generate a clear and I hope concise picture of the bumble bee’s life cycle I have often glossed over interesting points and been a little overly reductionist in my description, if you’ve been interested in the story then I urge to find out more.

The book “The Natural History of Bumblebees: a Sourcebook for Investigations” by Carol Kearns and James Thomson is a great resource. It contains enough information for an enthusiastic layman to get a good grasp of bumble bee biology and includes a “photographic filed guide” to American bumble bees for next summer. If you become utterly obsessed with bumble bees the book describes how to raise a nest by catching a queen before she established her own and how to use that nest to conduct simple experiments.

The Bumblebee Pages maintained by Laura Smith are an absolute mine of information. Discover the bumble bee and the UK’s Natural History Museum’s Bombus site are also worth a look.

Posted by David Winter 1:22 am

4 Comments:

interesting Thank you

Anonymous, at 11:54 am, April 19, 2007

I like this kind of scientist tales... specially if you're posting about bees! They're interesting a we can learn a lot about their style. I think we can't ignore this explanations and the investigations are increasing our knowledge about this insects.

Viagra Online, at 3:41 am, February 12, 2011

This is really interesting how those bees work all together in order to achieve their purposes, that's incredible if human beings work in the same way as bees they'd be more proactive.

Viagra versus Cialis, at 5:16 am, October 04, 2011