Oxygen clue to demise of prehistoric giant insects

THE emergence and decline of gigantic flying insects millions of years ago may have been linked to the amount of oxygen available to their water-breathing young, new research suggests.

Scientists studying the smaller modern-day descendants of the huge creatures, which included dragonflies with wingspans of almost a metre, believe they have solved a question which has puzzled experts for more than 100 years by looking at their larvae, which live in water.

They believe that larvae 300 million years ago took advantage of the higher oxygen levels available, using it to help fuel their growth to the size shown in fossilised remains.

When the climate later changed and the oxygen level dropped, the larger species' larvae could not take in enough of the gas to survive and the species went extinct, leaving only their smaller relatives alive.

Dr David Bilton, of Plymouth University's School of Marine Science and Engineering, who carried out the research, said: "In prehistoric times, higher levels of oxygen may have favoured the evolution of giant insects largely through their effects on larvae, and it is perhaps no accident that many extinct giants had aquatic juvenile stages."

In their paper, published in the Public Library of Science, Dr Bilton and Dr Wilco Verberk show that aquatic insect larvae are more sensitive to fluctuations in oxygen levels than the air-breathing land-based adults.

Though a link between oxygen levels and giant insects has been suggested before, no one has provided firm evidence of how they are linked.