Sticking to surfaces and walking up walls are so commonplace among insects that they risk becoming boring. But the green dock beetle has a fresh twist on this tired trick: it can stick to surfaces underwater. The secret to its aquatic stride is a set of small bubbles trapped beneath its feet. This insect can plod along underwater by literally walking on air.
The green dock beetle (Gastrophysa viridula) is a gorgeous European resident with a metallic green shell, occasionally streaked with rainbow hues. It can walk on flat surfaces thanks to thousands of hairs on the claws of their feet, which fit into the microscopic nooks and crannies of whatever’s underfoot. Most beetles have the same ability, and some boost the adhesive power of their hairs by secreting a sticky oil onto them.
These adaptations work well enough in dry conditions, but they ought to fail on wet surfaces. Water molecules should interfere with the hairs’ close contact, and disrupt the adhesive power of the oil. “People believed that beetles have no ability to walk under water,” says Naoe Hosoda from the National Institute for Material Science in Tuskuba, Japan.