A recent study challenges the long-held belief that prehistoric insects grew to giant sizes due to higher oxygen levels in the Earth's atmosphere. These ancient insects, like dragonflies with wingspans up to 27 inches, were thought to thrive due to a period when oxygen levels were 45% higher than today's. However, new research published in *Nature* shows that oxygen in the flight muscles of these insects was not the limiting factor for their size. Instead, the study found that their tracheal system, which transports oxygen, could expand without any significant structural limitations. The research led by Edward Snelling at the University of Pretoria indicates that the distribution of oxygen in the insect body wasn’t a bottleneck for their gigantism. While oxygen could still influence body size in other ways, the findings suggest that factors like predators or the insect exoskeleton may be responsible for their large size. This study overturns decades of speculation and leaves the mystery of why prehistoric insects grew so large unsolved.