Not much stops a cockroach in its tracks. They determinedly negotiate most obstacles they encounter. But how do cockroaches sense their surroundings?This is the question that puzzled Cynthia Harley, Brittany English and Roy Ritzmann from Case Western Reserve University. Knowing that many insects use their antennae and eyes to help them navigate obstacles, the team focused on the cockroach antennae to find out how they use them when negotiating vertical obstacles. Filming cockroaches with full-length, shortened and removed antennae as they encountered either an 11.7 mm high block or a glass shelf at heights ranging from 8.9 to14 mm, the team painstakingly analysed the insects'approaches and strategies for negotiating the obstacles when they could see under various lighting conditions and when they were wearing eye patches(p. 1463).
Watching the insects with full-length antennae, the team saw that the cockroaches almost always mounted the block successfully in a single step when they were within 11 mm of the block. The insects could estimate their distance from, and the height of, the obstacle using their antennae, allowing them to lift their front legs high enough to climb onto the obstacle. However, when the cockroaches' antennae were removed, the animals resorted to brute force,either ramming themselves into the block until they forced themselves up and over, or waving their front legs around until they encountered the top of the block, confirming that sensory information from the antennae is essential for cockroaches to overcome obstacles.
Analysing the insects' approaches to the glass shelf, it became clear that sensory inputs from the antennae were critical in the insect's decision to climb over or under the shelf. However, the lighting conditions also had a big effect on the way the cockroach dealt with the obstacle. The insects preferred to tunnel under the shelf in the light, `suggesting that the light created a context around this behaviour,' says Harley and the team.
So sensory inputs from the antennae provide vital information that helps cockroaches successfully negotiate obstacles.