This might look like a mascara brush or some tentacle-clad sea cucumber, but this is actually an image of a tongue. As you may have guessed, this is no ordinary tongue. Researchers call it a "hemodynamic nectar mop," and it belongs to a particular species of nectar-feeding bat called Glossophaga soricina. These bats feed on the nectar of flowers, hovering in front of the blooms and lapping up the sweet liquid inside. Scientists had long assumed the hairlike structures on bats' tongues were just that: static, unmoving hairs. But other nectar-feeding species like hummingbirds unfurl dynamic, branching tube structures on the tips of their tongues, and it got scientists thinking: Is there more to bat tongues than meets the eye?
Nectar-feeding action of bat (Glossophaga soricina). Image courtesy of vitor_barao/Flickr Using high-speed video, the researchers saw for the first time how a bat's tongue really works during feeding. When a bat sticks its tongue inside the flower, it slips in easily. Once inside, the tip of the tongue elongates, stretching from five millimeters to eight. The real surprise, though, was in the bats' tongue hairs, which they call "dynamic erectile papillae." Most of the time these papillae lay limp and flat against the tongue. But the researchers found that when a bat finds a juicy flower to feed from, the papillae jump to attention. As the tongue stretches, veins at the base of each hair fill with blood, causing the hairlike structures to swell and stand up. The change happens fast; it takes these tiny soldiers just 0.04 seconds to spring to attention. Nectar gets trapped between the rows of papillae, allowing the bat to pull out a much larger droplet of nectar each time it sticks its tongue in the flower. This is particularly important since the hovering required to feed takes up a lot of energy. The highly textured surface makes the lapping process much more efficient for the bat, and since the papillae lay flat when not in use, they don't get in the bat's way when it's not feeding. In addition to understanding nectar-feeding efficiencies, the researchers say their findings have potential applications in the medical realm, too. They say the bat tongue could be used as a model to develop soft, flexible and dynamic robotic tools. With the hair-like structures laying flat, these tiny surgical implements could be used to navigate through small spaces like blood vessels or access hard-to-reach parts of the body, such as the intestines. Once in place, these tools could be inflated with air or liquid, much like the bats' papillae. Such bat-inspired tools could ultimately be used to conduct surgeries like angioplasty (to reopen blocked or narrowed arteries) or gastric endoscopy (to peer inside the organs of the digestive system). The findings
were published today in the Proceedings of the National Academy of Sciences, along with videos
of the bats' impresive tongues.
The tip of the tongue turns red as blood fills the papillae. Diagram (and top image) courtesy Harper et al./PNAS