A flexible joint in the middle of a bumblebee's wings enhances aerodynamic lift, thus allowing the insects to carry more nectar and pollen when they forage, a new study suggests. Scientists have long known that some insect wings bend and twist during flight, but the benefits of that flexibility have been uncertain. In the first-ever tests of the potential plus-side of wing flexibility in living insects, researchers strapped a small harness to bumblebees, attached a beaded string to it, and then measured how much weight the insects could lift when flying (see video above). For some bees, the team stiffened the insects' wings by supergluing a small piece of glitter atop a key joint in the middle of the wing membrane. Others flew unencumbered. (To ensure that the glitter didn't affect flight performance simply by adding weight, the researchers glued a piece to an inflexible portion of the insects' wings on other bumblebees.) Analyses showed that immobilizing the flexible joint stiffened the wing by 37% and led to an 8.6% reduction in the amount of weight a bumblebee could carry, the researchers report online today in the Proceedings of the Royal Society B. Because the presence of glitter didn't change either the size of the insects' wing strokes or the frequency at which the bees flapped, the team attributes the decrease in lift capacity to the loss of wing flexibility. Computer models suggest that wing flexing helps swirls of air generated by the leading edges of each wing remain in close proximity to a wing's surface as the air flows across it, thereby boosting aerodynamic lift—a trick that designers of insect-mimicking flying robots should pay heed to.
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