Proc. Natl Acad. Sci. USA doi:10.1073/pnas.070864105 (2008)

Credit: ELLEN D. CURRANO

Hungry herbivorous insects thrived during a period on Earth when temperatures and carbon dioxide levels soared, according to a new study, which could foreshadow a surge in swarming pests. Scientists believe that the Paleocene–Eocene Thermal Maximum (PETM), an event that occurred 55.8 million years ago, is one of the best analogues of current climate change and could hint at what lies ahead.

Ellen Currano of Pennsylvania State University and co-workers examined over 5,000 fossil leaves from Wyoming's Bighorn Basin for the telltale holes and galls left by different types of ancient insects. Recently discovered fossils from the abrupt warming event were compared with leaves that fossilized earlier or later. As temperatures rose, the authors found, so did the frequency of damaged leaves and the diversity of insects whose damage patterns could be identified.

The ravaging insects may have first followed tropical host plants whose ranges were expanding with increasing temperature, before spreading to northern plants, the scientists say. Some insects, however, apparently arrived under their own steam, before plant diversification was underway. In our rapidly warming world, say the researchers, ecological disruption on a similar scale can be expected.