Harking back to two days ago – giant insects. They seem to have reached their maximum size during the Late Carbiniferous – which is why they turn up in coal seams, and the early Permian. Giant dragonflies with a wing span up to 28 inches are pretty fearsome, hence the coining of the term, the Beast of Bolsover (found in a coal mine in Bolsover). The theory is that high oxygen concentrations in the atmosphere allowed insects to grow to an abnormal size. A paper in PNAS, by Matthew Clapham and Jerad Kar, see http://phys.org/print258035891.html, involved compiling a large dataset of wing lengths from published sources of fossil insects in an attempt to prove high oxygen really was to blame. In the Cretaceous, some 150 million years ago, oxygen again went up – but this time insects did not grow to outlandish proportions. It is suggested that the evolution of birds, at this time, played a role – being small was more manoeverable and there was a greater chance of getting away. However, all is not as simple as it seems as although small insects were still around in the Carboniferous and the Permian there is apparently a gap in the fossil insect record. This inhibits the search for precisely when insects downsized, and the question of whether or not it occurred in stages. The question might then be asked – what event wiped out the large insects?