When the tiger beetle runs full speed, it can no longer see where it's going. To stay on course while running, the beetles rigidly hold their antennae directly in front of them to mechanically sense their environments and avoid obstacles, according to a study published online in the journal Proceedings of the Royal Society B.
The findings raise questions about how other speedy animals, such as birds of prey and some fish, sense their environments when moving quickly. The study also reveals that little is known about the mechanism behind environmental detection by the insects' antennae. "For an insect with really good vision that is active in the daytime normally, you would think it would not rely on antennae for sensing its environment," said Cole Gilbert, a professor of entomology at Cornell University and the paper's senior author.
"It has evolved important mechano-sensing behavior while running because it runs so fast," Gilbert added.
"Gilbert and Zurek sought to learn how the running insects negotiate obstacles in their habitat, such as crevasses or grass stems, and what role their characteristically forward antennae play. To test this, the researchers set up a runway with a hurdle: In one experiment normal tiger beetles (of the species Cicindela hirticollis) ran the track and negotiated the hurdle, tilting their bodies up when their antennae touched the hurdle; in a second experiment, the researchers painted over the beetles' eyes and found these blind beetles responded similarly. In the third test, they clipped the antennae of sighted beetles, and the insects smacked right into the hurdle," a press release announcing the findings stated.
The experiment revealed that for fast-moving tiger beetles, "eyes are not sufficient or necessary to avoid obstacles," Gilbert said. "The antennae are held extremely rigid with the tips 1.5 millimeters off the ground, so they would potentially pick up any discontinuity in the surface."
Gilbert questioned how certain falcons and predatory fish compensate for blurred vision while on the hunt, potential research areas that no one has tested.
Watch a video of tiger beetle testing here.