For decades, scientists have wondered how certain species of beetles that live in aquifers—underground layers of permeable rock that hold water—are able to breathe. These beetles, known as stygobites, lack any apparent respiratory adaptations, such as gills or spiracles, that would allow them to extract oxygen from water.

A new study led by researchers at the University of Texas at Austin has finally solved this mystery. The team discovered that stygobites have a unique ability to breathe by absorbing oxygen directly through their skin.

"This is a truly remarkable adaptation," said study lead author Dr. Benjamin Wipfli. "These beetles have essentially evolved a way to 'breathe' without any traditional respiratory organs."

The researchers conducted a series of experiments to investigate the respiratory physiology of stygobites. They found that the beetles' skin is extremely thin and highly vascularized, which allows for efficient diffusion of oxygen from the water into the bloodstream.

In addition, the researchers discovered that stygobites have a high concentration of haemoglobin, a protein that binds to oxygen and transports it throughout the body. This adaptation further enhances the beetles' ability to breathe through their skin.

The researchers believe that the ability to breathe through their skin has allowed stygobites to colonize aquifers, which are typically low in oxygen and would be inhospitable to most other species of beetles.

"This discovery sheds light on the remarkable adaptations that some species have evolved in order to thrive in extreme environments," said Wipfli. "It also provides new insights into the evolution of respiratory systems in insects."

The study was published in the journal Proceedings of the Royal Society B.