Saturday, November 28, 2009

Pollen Baskets (Corbicula)


Common Eastern Bumble Bee - Bombus impatiens
(Photo:  Marvin Smith on 11/8/09)


Most everyone knows that bees visit flowers and collect nectar. Humans value the nectar product and call it honey. Bees also collect pollen. To the bee, pollen is as important as nectar. Pollen is the primary food for developing bee larvae.

Female bees (queens and workers) in family Apidae (honey bees, carpenter bees, bumblebees and several lesser known groups) have specialized structures called pollen baskets (corbicula) used for temporarily storing collected pollen so it can be transported back to the nest/colony. The pollen basket is a smooth, concave structure surrounded by long, stiff hairs located on the tibia of the bee's two rear legs. As the bee visits flowers, she accumulates pollen all over her body. She uses her legs to aggregate the pollen and transfer it to her pollen basket. It may look as if a bee simply has hairy legs, but some of those hairs (setae) are actually combs and brushes used for transferring pollen. The pollen is combed, pressed, compacted, and transferred to her pollen basket. Honey and/or nectar is used to moisten the dry pollen so it will stay in place.


Bumblebee with loaded pollen basket.
(Photo:  Beatriz Moisset via Wikimedia)


While most all bees collect pollen, not all bees have pollen baskets. Many have scopa, a general term referring to a number of different pollen-carrying modifications on the body of a bee. In most bees, the scopa is simply a particularly dense mass of elongated, often branched, hairs (or setae) on the hind leg.


Halictid bee, scopa loaded with pollen.
(Photo:  Beatriz Moisset via Wikimedia )


The bumblebee in the photo at the top of the page is a Common Eastern Bumble Bee (Bombus impatiens), probably the most often encountered bumble bee in eastern North America. It has an unusually long flight season and thrives across a wide range of habitats and climates ranging from the cold temperate zone (e.g., Minnesota) to the warm subtropics (south Florida). B. impatiens can be found in rural, suburban and urban environments. There are isolated pockets of Common Eastern Bumble Bees outside of it's normal range -- like California -- because it escapes from commercial greenhouses where it is used for pollination. The bee has no pollen because this photo was taken in early November when pollen sources were few and far between. She was lucky to find a few scraggly zinnias still blooming in our garden.

Sources and links:
Bombus impatiens on BugGuide
Pollen Basket on Wikipedia
Scopa on Wikipedia
Bumblebee legs on Bumblebee.org







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20 comments:

alwaysbcmom.com said...

Lovely photos! Thanks for all the information.

ramblingwoods.com said...

These are wonderful photos and explanations.. I know that pollinators are in trouble, but I didn't know the mechanics of collecting the pollen...Thank you for participating in Nature Notes Marvin. I appreciate it... Michelle

ellen said...

Nice catch! Mine is up. Hope you can drop by to view my very first entry. Your visit is a blessing. God Bless!

http://www.ellenheartbeats.com
http://www.ellentinytreasures.com
http://mariellewhatmattersmost.blogspot.com

SAPhotographs (Joan) said...

A wonderful post Marvin. Love the pics too.

eileeninmd said...

Wonderful closeups of the bees and the flowers looks so pretty.

Lisa at Greenbow said...

Great photos and information Marvin. While I often see bees in the garden with their little pollen baskets full I didn't know much about them. It will be a long time until we see this again.

AphotoAday said...

Really nice focus job on that, Marvin...

Wren said...

You're lucky to have real bumblebees. Plus, you got a great photo.

Crafty Green Poet said...

I love bees knees! This is a very interesting post. Do you know if the colour of the pollen baskets varies with the species of bee or the diet of bee? This summer I was one day watching three different species of bee on a bush and they all had different coloured knees so I thought this might be specific to the species, but a beekeeper I know said its only diet that affects the colour of the knees, but this seemed to contradict my observation seeign as my bees were all on the one bush.... any ideas?

Lana Gramlich said...

And despite their cute-fuzzy appearance, I found out they're among the more aggressive bees (outside of Africanized, of course.) Fortunately I didn't learn that the hard way!

MObugs said...

Wonderful post Marvin, lots of valuable information about the abilities of these great insects. I have always been fascinated by their ability to get airborne after greedily loading up on pollen. I've seen some with legs so laden with pollen they remind me of chipmunks when they fill their pouches afraid that another meal won't be forthcoming. The first photo is beautiful!

Marvin said...

Juliet: I really don't know the definitive answer to your question. What little I do know agrees with the beekeeper. Color will vary depending upon the flowers visited. However, there may also be species variations of which I'm not aware.

Crafty Green Poet said...

Marvin I've just had an email from Bumblebee Conservation who said that the colour variation in pollen baskets is all due to the food plants, so my three species with three differetn coloured pollen baskets must have been just co-incidence!

Marvin said...

Juliet: Another bit of related information. If the bees you saw were bumblebees, seeing three that had been collecting different pollen on the same plant is a little unusual. According to Bumblebees.org, individual bees tend to specialize in particular flowers. This is because the bees must learn how to get to the nectar/pollen in each flower species. With open composite flowers this is not a problem, but more complex flowers present a challenge to the bee. Once a bees has learned how to access the nectar/pollen in a particular flower, it tends to keep visiting that same flower species as long as they are available. This is the reason bumblebees are considered excellent pollinators. By sticking with the same species, the bee does a great job of pollination. Bees that visit a wide variety of flowers do some pollination, but they also spread around a lot of useless pollen between species.

Crafty Green Poet said...

interesting comment there Marvin, so that makes the whole thing possibly more intriguing.... bees are endlessly fascinating....

WR said...

Hi Marvin:

Were these recently taken? I've not seen any bees for quite a while. Perhaps they need raincoats here. Wonderful shots...flowers are as excellent as the bees! Have you noticed a decline in bee activity in your neck of the woods?

Sandy Kessler said...

rich color sady

Marvin said...

WR: I took the top bumblebee photo in early November. (The others are stock photos. I don't really know when they were taken.) We had a mild fall. I saw bees of one sort of another just about every time our temperature warmed up throughout November. However, we've finally had temps as low as 19°F, so that's probably the end of our bees until spring.

In general, I haven't noticed a decline in our bee population, but without careful record keeping, a gradual decline would probably be hard to notice.

√ Abraham Lincoln said...

I spend a lot of time in the summers just looking for the colors of pollen the bees collect. I am always amazed at the big difference.

Carol said...

I love your Bumblebee. The low clouds reminded me of a hilltop I used to live on in NY. I would be in sunshine and all around me clouds.

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