Meeting Abstract
Cockroaches possess an almost unparalleled tenacity to squeeze through the smallest cracks. To quantify cockroaches’ capacity to traverse crevices, we ran, Periplaneta americana, through a rectangular acrylic tube with a vertically adjustable gate at 3.2, 4.4 and 6.1 mm crevice heights. We discovered that cockroaches traversed crevices as small as 3 mm, the height of two stacked US pennies, by compressing their body segments 40-60%. Crevice traversal was rapid (288–821 ms) and appeared continuous in real time. However, high-speed videography revealed a complex behavior involving several stages – exploration and crevice detection, head traversal with entry and body reorientation, followed by pronotum, thorax and abdomen traversal. The time taken from head entry until abdomen tip exit increased with a decrease in crevice height from 6.1 to 3.2 mm. Traversal time was similar for 6.1 and 4.4 mm crevices (0% and 27% abdomen compression, respectively), but significantly longer at 3.2 mm (47% abdomen compression), approaching the limit of performance. The probability of successful crevice traversal decreased significantly with a decrease in crevice height from 72% at 6.1 mm to 17% at 3.2 mm. Turning back during a trial was the dominant failure mode suggesting that animals seek alternate routes if crevices are too small. Animals were never trapped in the largest crevices, but occasionally became stuck at the smallest crevice heights (9%) during thorax traversal, a potentially fatal event in nature if exposed to predators. The compressibility of the abdomen reduced the normal load on the body enabling animals to generate thrust sufficient to successfully negotiate the crevice. Cockroaches traversing crevices provides inspiration for soft search-and-rescue robots that can penetrate rubble.
