Most bees use their tongues to lick nectar from flowers. But a new study shows that tropical orchid bees have opted out of a life of lapping and gone for sucking instead. This unique skill helps them to feed on runny nectar in deep flowers, and it may have helped drive the evolution of the flowers as well.
If you watch a cat slowly lap up a saucer of milk, you'll know what an inefficient tool a tongue is for drinking a thin liquid. This is how the ancestor of orchid bees must have felt when it began frequenting the flowers of spiral gingers and other plants in tropical forests. These deep flowers produce nectar that is less concentrated--and thus less sticky--than the stuff that honeybees lick up with their tongues.
All bees have a tubelike proboscis, says evolutionary biologist Brendan Borrell of the University of California, Berkeley. But in all bees previously studied, the proboscis isn't used for sucking. It's the tongue, which sits inside the proboscis, that does the work. But when Borrell surgically removed the tongue from orchid bees of the species Euglossa imperialis, he found that the tongueless bees were no worse at drinking nectar. This shows that the bees have given up on their tongues in favor of their proboscises.
To find out why they prefer sucking over lapping, the researcher made fake flowers out of cardboard and styrofoam with a tube of syrup in the middle. He let 71 male bees ("easier to catch and they don't sting," says Borrell) drink various dilutions of the syrup, ranging from watery 5% dilutions to the 75% consistency ideal for pancakes, and measured how quickly they could drink them. Orchid bees were best at dealing with 35% solutions, which is exactly the sugar concentration of nectar that the animals collect in the wild, whereas lapping species, such as honeybees, prefer more syrupy nectar, with a sugar concentration of around 55%, Borrell reports online this week in Biology Letters.
Borrell thinks the orchid bees and their flowers may have evolved hand-in-hand, with the flowers getting deeper with runnier nectar, and the bees evolving longer proboscises. (Euglossa imperialis's proboscis is longer than its body.) Bee researcher Sydney Cameron of the University of Illinois, Urbana-Champaign, thinks the new study is "really neat." If it were confirmed that all orchid bees behave this way, it would put them in a unique category, she says.