Insects cut down to size by birds

The evolution of birds may have helped to keep insects from growing into much larger species, scientists have said. Faced with an airborne predatory threat, the creatures stayed small to be more manoeuvrable, it is believed.

Throughout earth's history, giant insects evolved during periods when the atmosphere was rich in oxygen. They reached their largest size about 300 million years ago, when dragonfly-like creatures called griffinflies, with wingspans up to 28 inches wide, ruled the sky.

Researchers at the University of California at Santa Cruz concluded when birds first appeared, the insects' need to be nimble in the air rose, leading them to develop smaller bodies. The study is published in the journal Proceedings of the National Academy of Sciences.

Dr Matthew Clapham said insect size reduced 150 million years ago, "and this coincides with the evolution of birds".