“You see lots of little creatures zipping about in the water,” said Karl Jones, a graduate student at the University of Adelaide in Australia and an author of the new paper. “We’re able to put small nets down these boreholes, which are only about 35 millimeters in diameter, and catch the animals swimming around in the water.”

After carefully bringing the beetles back to the lab, the researchers put them through a series of tests.

Some of the beetles they looked at under an electron microscope to get a sense of the topography of their outsides. Strictly speaking, beetles don’t have skin. Instead they’re covered in what’s called a cuticle (not the same as the skin layer on your finger), a stiff layer of outer tissue. Some species have structures like hollow hairs on their cuticles that allow them to pull oxygen from the water into their respiratory system. But the three species examined in this study lacked such structures.

However, when the scientists glued the beetles to the end of a wire, submerged them and monitored the oxygen content of the surrounding water, they observed something curious. The closer the sensor got to the beetle, the lower the oxygen reading. This suggested that the beetles were somehow drawing the oxygen out of the water immediately around them.

“It’s going right through the cuticle, either right into the respiratory system or directly into the tissue,” Mr. Jones said. This strategy has been seen before in insect larvae that live underwater, but not yet in mature beetles.