We've talked a bit about gigantic dragonflies found in the fossil record from the Carboniferous period. I mentioned that a recent study on oxygen limitation in insects suggests that the leading theory about these giant arthropods - that they got big because the high levels of O2 made it possible - may not be correct. Interestingly they propose that young insects HAD to grow large to avoid oxygen poisoning.
(the National Geo article, which is also the source of the photo
above). The original research article by Verberk and Bilton in PLoS ONE
Verberk WCEP, Bilton DT (2011) Can Oxygen Set Thermal Limits in an Insect and Drive Gigantism? PLoS ONE 6(7):