A strong gust of wind can throw even an adult off the path for a short time. So how do lightweight flying insects, which should be thrown off course by the slightest breeze, manage to fly stably?
Life at dizzy heights is a constant challenge to insects' flying skills - even the slightest draft threatens to send these lightweights into a spin. Then, instead of a soft landing, a hard impact awaits. The Diptera, like flies and mosquitoes, therefore quickly converted their hind wings into two tiny, clapper-like flight stabilizers, the Schwingkölbchen or H alteren. These vibrate in unison with the wings and the insect responds with a lightning-fast position correction if the holders are deflected just a little from the normal oscillating path.
Nice and good for the diptera - but why don't four-winged insects like butterflies that lack these extremely useful vibrating flasks fall off? Even more so when they are crepuscular and can no longer use their eyes to control their course? A research team led by University of Washington Sanjay Sane, led by Thomas Daniel, chose the tobacco hawkmoth (Manduca sexta) to uncover further aids to flight. It couldn't be converted hind wings, after all M. sexta uses four magnificent wings for air locomotion. So Sane took a closer look at another paired structure: the hawk moth's antennae.
Sane and his colleagues filmed the flying animals with three high-speed cameras placed at right angles to each other. With the help of this arrangement, the scientists realized that the antennae of the tobacco hawkmoth vibrate in unison with the wings, just like the antennae of the diptera, and that they are easily deflected from their plane of vibration with changes in body position. The hawk moths actually perceive these tiny changes with special organs at the base of the antennae, as the researchers verified with electrophysiological measurements. Accordingly, in the case of the four-winged hawkmoth, the antennae take over the flight-stabilizing function, which the vibrating flasks have in the case of two-winged hawk moths.
Now the research team wanted to know whether the antennae work according to the same principle as the holders of the Diptera, or whether other stimuli such as scent, moisture or temperature, which the insects register via the feelers, play a role. To do this, they cut off the feelers of some animals just above the base, sent them into a flight chamber and observed the flying skills of the butterflies.
The amputated hawk moths were suddenly severely impaired: they constantly bumped into the walls of the chamber or even fell - comparison specimens with intact antennae, on the other hand, flew error-free. But when the scientists stuck their feelers back on the amputated insects, they suddenly steered through the air almost as well as intact hawk moths. Since the nerve tracts that transmit other information such as scent or moisture remained cut when the antennae were attached, it was clear that the movement of the antennae, which is registered at the base of the antennae, alone is sufficient to stabilize the moth's flight.
At least the tobacco hawkmoth, but possibly also other four-winged insects, have given their antennae another function: as multifunctional antennae, they guide the animals safely and dexterously through the turbulent air.