ANYONE who has tried to swat a cockroach will know those insects’ strange ability, in the heat of pursuit, to disappear. Robert Full and his colleagues at the University of California, Berkeley, have now worked out how they do this—and taught a miniature robot to copy the feat.
Dr Full had been using high-speed photography to study how cockroaches employ their antennae to sense and cross gaps. When the researchers made the gaps wider, they saw the animals flipping back underneath the ledge at the edge of the gap, rather than jumping across the empty space. As they report in the Public Library of Science, cockroaches running towards a gap suddenly grip the edge with the hooklike claws on their rear legs and swing 180° to land firmly underneath the ledge, upside down. They can pull off this stunt in a fifth of a second—so fast that the animals’ bodies are subject to between three and five times the force of gravity, and also so fast that the movement is invisible to the human eye.