Alfalfa: How the Plant World’s Little Bunny Foo Foo Bops Bees

The leafcutter bee has evolved to deal well with the alfalfa flower's defense mechanism. Peggy Greb/Wikimedia Commons

Turns out children's song star Little Bunny Foo Foo isn't the only cute thing that bops unsuspecting critters on the head. As if taking a page out of Foo Foo's songbook, alfalfa flowers have been spotted bopping honeybees as defense when the bees try to take the flowers' nectar and pollen.

Here's how the tripping (that's the official term for the process) mechanism works: To get at the alfalfa nectar and release the pollen, honeybees have to press their heads against the petals until the male and female parts of the flower are exposed – but when that happens, the flower smacks the bee in the face. Check out the video below that demonstrates the trip mechanism – think of it as a spring-loaded attack along the same lines as a mousetrap. 

Are these alfalfa attacks behind the reported decline in honeybee populations? Nope. In fact, it's the alfalfa that suffers, rather than the bees. As the honeybees learn that the alfalfa flowers will bop them on the head, most also learn to leave those flowers alone and go for the easier nectar of some less-aggressive flower. A few of the honeybees learn to get to the nectar without tripping the flowers, bypassing the whole pollination mechanism, which also keeps the alfalfa seed from spreading as easily.

Alfalfa is commonly grown as feed for horses and cattle, so it's essential to the food chain that the flowers get pollinated. Fortunately for carnivores everywhere, other bees are more effective than honeybees at tripping the plants. For more efficient pollination, commercial alfalfa growers generally don't use honeybees, or use them in combination with two other bee species: the alfalfa leafcutter bee, a Eurasian bee first found in the U.S. in the 1930s; and the alkali bee, an alfalfa pollinator native to the United States. 

Both of these bee species are larger than honeybees and actually dig into the plants to forage for the pollen rather than the nectar that the honeybee's after. In addition, they don't seem to mind being smacked. All of these combine to make them more efficient pollinators for alfalfa than the honeybee.

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