Brushes on Midlegs Clean Off the Forelegs

Biological Strategy

Bees

Holly Kerstiens

Image: Almer Steegstra / Shutterstock / Some rights reserved

Expel Solids

Living systems must often discharge solids–such as seeds, eggs, pollen, and mineral salts–for reproduction, protection, or other reasons. Solids can be easily moved when a living system applies force to them. But creating that force requires energy, so living systems must either have efficient strategies worth the energy investment or use an outside force (such as gravity). For example, a tropical mistletoe positions its pollen so that the weight of a bird landing nearby triggers the pollen’s release onto the bird’s forehead. The bird then fertilizes other mistletoes that it visits.

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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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Bees use brushes on their midlegs to clean off pollen and dirt from their forelegs by pulling their forelegs between their midlegs.

The last large segment on the middle leg of the bee is known as the midleg basitarsus and it often contains a brush made of hairs. This brush can be used for grooming as the bee forages. The brush cleans off the forelegs as the bee flexes, pulling the foreleg between the basitarsus and the femur to trap pollen and dirt.

The hairs making up the brush can be different lengths, straight, bent or even hooked. Notice the differences in the brushes of the bees above.

This information is also available from the University of Calgary Invertebrate collection, where it was curated as part of a study on design inspired by bees.

Image: Sam Droege / Public Domain - No restrictions

The midleg of Megachile fortis.

Image: Wayne Boo / Public Domain - No restrictions

The midleg of Megachile petulans.

Image: Dejen Mengis / Public Domain - No restrictions

The midleg of Melissodes apicata.

Image: Sam Droege / Public Domain - No restrictions

The midleg of Megachile sculpturalis.

Last Updated April 3, 2019

References

“The foreleg is cleaned (or pollen is transferred from it to the middle leg) by drawing it through the flexed (at femorotibial joint) middle leg ( Jander, 1976). This movement is not seen in other Hymenoptera. It is associated in females and some males with the midfemoral brush, a brush on the lower side of the middle femur- trochanter, and the midtibial brush, a brush of often ordinary hairs on the lower side of the middle tibia and sometimes basitarsus. When the leg is flexed, these brushes are opposable and both surfaces of the foreleg are cleaned at one stroke.” Michener, 2007:61

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The Bees of the World, Second Edition.

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