Hairy Hind Legs Carry Variously-sized Pollen

Biological Strategy

Mining bees

Jeanette Lim

Image: Martin Grimm / Flickr / Some rights reserved

Capture, Absorb, or Filter Solids

Some living systems must secure solid particles such as sediment, usually to keep the particles from hindering their health or activity. The most common way in which they do this is through filtering. To be effective, a filtering system must be appropriate to the sizes of solid particles to be captured and must capture only what is needed. It must also be effective in the appropriate media–air, water, or sometimes solids like soil. An example is mangroves, which are trees that grow along ocean coasts. Their root system slows down and settles sediment out of the water, building up soil to support the mangrove ecosystem.

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Store Solids

Living systems, especially organisms, must sometimes store solids, often pieces of material (such as mud, seeds, stones, or leaf fragments). They use these solids for building structures, feeding during periods of low food availability, or other purposes. To be effective, the storage strategy must be appropriate to the sizes of solids and to the media in which they exist, whether air, water, or other solids like soil. It must also safely arrange the solids for storage in a location appropriate to either short- or long-term storage. An example is the Clark’s nutcracker, a forest bird that can collect up to 150 pine seeds and temporarily hold them in an expandable pouch under its head, where it doesn’t interfere with the bird’s daily activities.

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Insects

Class Insecta (“an insect”): Flies, ants, beetles, cockroaches, fleas, dragonflies

Insects are the most abundant arthropods—they make up 90% of the animals in the phylum. They’re found everywhere on earth except the deep ocean, and scientists estimate there are millions of insects not yet described. Most live on land, but many live in freshwater or saltwater marshes for part of their life cycles. Insects have three distinct body sections: a head, which has specialized mouthparts, a thorax, which has jointed legs, and an abdomen. They have well-developed nervous and sensory systems, and are the only invertebrate that can fly, thanks to their lightweight exoskeletons and small size.

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Hairy hind legs on bees can carry a variety of pollen sizes by mixing pollen grains with liquid.

Flower pollen is a major source of and nutrients that all bees need at some stage in their life cycle. Pollen collection is carried out only by female bees, which have specialized body parts that enable them to collect and transport pollen grains back to the nest. Modified parts of the female bee’s hind legs, for instance, are used to collect and store pollen externally. These structures are rows of small hairs (called scopae) or flattened plates rimmed with curved hairs (called corbicula) that function like brushes and baskets that can hold the dust-like pollen grains in place while the bee forages.

The size of pollen grains from different flowers can range from 5 to 210 μm, and pollen grain surfaces can similarly vary in their structure and texture. As a result, many species of bees specialize on a narrow range of flower types and pollen. The density and bushiness of the bees’ scopal hairs have been shaped through co-evolution to function best with specific sizes and shapes of pollen.

Other bees, however, can be more flexible in the types of pollen they collect. One strategy that enables this flexibility is mixing collected pollen with liquid, in the form of nectar, saliva, or floral oils. Moistening the pollen as it’s collected enables the grains to be packed and shaped together into a more concentrated package. Pollen-collecting structures on the bee’s legs needn’t be specialized to transport individual pollen grains; they can be more simplified and transport packages consisting of any size and shape of pollen. Female mining bees (of the family Andrenidae), for example, add nectar to their pollen to moisten it. The scopal hairs on their hind legs tend to be less specialized, too: they are short and sparse with moderate branching. Bees that feed on floral oils and pollen have long and stiff scopal guard hairs with a bushier underlayer of short, flexible, and branched hairs. In some species, this underlayer consists of separate hairs, and in other species, it consists of branches off the main long hairs. Both of these arrangements function the same: the bushy underlayer sops up oil, while the longer guard hairs hold onto the pollen.

Image: jacinta lluch valero / CC BY SA - Creative Commons Attribution + ShareAlike

Image: Louisa Howard, Charles Daghlian / Public Domain - No restrictions

Image: Gilles San Martin / CC BY SA - Creative Commons Attribution + ShareAlike

The triangular-shaped segment on the left with the fringe of hairs is the pollen basket (corbicula).

Wingbeat Vibrations Cause Pollen Release

Carpenter bees

The wings of carpenter bees cause pink gentian flowers to release their pollen by beating at a frequency that causes the anthers to vibrate.

Last Updated July 2, 2020

References

“The behavior of moistening pollen by adding nectar or oil to it as it is packed in an external transport apparatus allows a wide variety of pollen grains with different sizes and surface ornamentations to be transported by the same apparatus. Thus, the scope of female Panurginae (Andrenidae) and Melittidae that add nectar to their pollen loads consist of sparse, short, only moderately branched hairs.” (Thorp 1979:793)

Journal article

Structural, Behavioral, and Physiological Adaptations of Bees (Apoidea) for Collecting Pollen

Annals of the Missouri Botanical Garden, 66(4): 788-812 | 01/01/1979 | Thorp RW

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Reference

Book section

The Collection of Pollen by Bees

In: Pollen and Pollination. Dafni A, Hesse M, Pacini E, editors. New York (NY): Springer-Verlag Wien. p. 211-223. | Thorp RW

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