This butterfly has sensitivity

This butterfly has sensitivity

A pigeon tail drinking nectar © Anna Stöckl

Highly developed eyes and a complex brain enable our human hands to perform even difficult tasks, such as playing the piano or typing messages. But surprisingly, the little pigeon tail is also capable of similar sensitivity, as researchers have now discovered. Thanks to delicate trunk-eye coordination, the butterfly can target flowers and drink their nectar. This efficiency in mini format would also be interesting for robotics.

Reaching for a glass of water, typing something on the keyboard or using our smartphone may be everyday tasks for us humans, but in the realm of the nervous system they represent peak performance. Before we reach for something, we first have to capture its position in three dimensions in our environment and then pass this information on to our motor system, which ultimately controls the movement. During the movement itself, we also do all sorts of fine-tuning with the help of our eyes.

Due to this high level of neuronal “computing power”, invertebrates such as insects, with their simple, tiny nervous systems, were previously considered largely incapable of carrying out such complex movements. Rather, it was assumed that their movements were more automated and less sensitive. For example, when a praying mantis has spotted a prey animal, it always pounces on it in the same rocket-like movement and no longer steers. If the prey has dodged in the meantime, the attack will simply be in vain.

Straw acrobatics for pigeon tails

However, there are also insects that science has a little more confidence in, including the pigeontail (Macroglossum stellatarum). This moth looks like a mixture of a butterfly and a bird and is also native to this country. To get to flower nectar, pigeontails hover like a helicopter in the same place for a long time and then penetrate even tiny flower openings with their body-long proboscis.

“It’s like trying to hit the opening of a beverage can on the floor with a long straw while standing,” explains Anna Stöckl from the University of Konstanz, explaining the difficulty of this undertaking. She is the senior author of a research team that has just investigated how the pigeon swan achieves this delicate feat. To do this, Stöckl and her colleagues had the butterflies fly to artificial flowers and filmed them with a high-speed camera. This enabled them to determine the exact positions of the butterflies’ bodies, heads and trunks as well as their typical movements.

Lots of similarities with us humans

Stöckl and her team discovered that the pigeon tails use their trunks in a similar way to how we humans use our fingers. Because just like them, the trunk can only be moved sideways with difficulty, but it can move about one and a half centimeters forwards and backwards. The rough positioning of the proboscis in the flower is therefore done by the butterflies aligning their bodies accordingly in flight. Only then do the smaller movements of the trunk take over, with which the pigeons’ tails delicately feel their way and finally reach the nectar opening, the researchers report. Applied to us humans, this would mean that we first have to use our arm to get our hand into position and then use the delicate movements of the individual fingers to reach for a glass, for example.

And there is another similarity between humans and pigeontails: Just like us, the butterflies apparently need their eyes as a consistent source of visual information in order to maneuver their trunks precisely. If these were covered in the experiment, the butterflies’ movements were much more aimless and they took considerably longer to find nectar. Unlike the praying mantis, which attacks once and then always carries out the same movement, pigeontails continuously adjust their movements using their eyes, explain Stöckl and her colleagues.

The sensitivity of the pigeon tails not only rehabilitates the group of insects in terms of their cognitive abilities, but could also help in the development of robots in the future. “In order to drink nectar, the insects have to make do with a tiny fraction of the processing capacity that is available to our nervous system, for example,” explains Stöckl. Such a small but extremely efficient brain is also in high demand in robotics. However, exactly how the pigeontail’s brain achieves its high performance has not yet been finally clarified.

Source: University of Konstanz; Specialist article: Proceedings of the National Academy of Sciences, doi: 10.1073/pnas.2306937121

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