For a long time, scientists believed that high levels of oxygen allowed giant prehistoric insects to grow in size. This idea shaped our understanding of ancient life, but new research is shaking things up. A recent study published in Nature suggests we might need to rethink how we explain the size and existence of these enormous insects.
About 300 million years ago, Earth looked very different. The supercontinent Pangaea dominated the globe, covered by lush coal forests. This environment was home to a variety of life forms, including giant invertebrates in the skies.
In the 1980s, experts started connecting giant insects to the atmosphere’s oxygen levels. A study from 1995 noted that oxygen peaked during the same period that large insects appeared in fossil records, leading scientists to believe that oxygen allowed these insects to grow larger than modern species.
Insects breathe through a network of tiny tubes called tracheae, which deliver oxygen directly to their muscles. This system means that as insects grow, oxygen might not reach all their parts efficiently, particularly the flight muscles that need a lot of energy.
However, the new study led by Edward Snelling from the University of Pretoria took a closer look at insect flight muscles using advanced microscopy. They discovered that tracheoles, which transport oxygen, take up only about 1% of muscle volume. Even for giant insects, this space is relatively small.
Snelling noted, “If atmospheric oxygen sets a limit on maximum insect size, there should be evidence of compensation in tracheoles.” While there is some compensation in larger insects, it is minimal. This challenges the long-held belief that oxygen delivery constrained their size.
Yet, the mystery remains unsolved. Although the study undermines a major part of the oxygen theory, it doesn’t eliminate oxygen’s potential role entirely. Other factors could also influence insect size, such as their respiratory system or their interaction with other species.
Roger Seymour, a researcher from the University of Adelaide, emphasized that birds and mammals have a far greater space devoted to oxygen transportation than insects do. If oxygen were truly a limiting factor for insect size, there seems to be considerable room for evolutionary growth in tracheoles.
Additionally, other explanations for why giant insects thrived—but later diminished—are emerging. Predation by vertebrates might have kept their sizes in check. Or, it could be that the structure of insect exoskeletons sets natural limits on how big they could grow.
Even today, scientists are piecing together the factors that allowed ancient insects to flourish and later fade away. According to recent studies, many people on social media remain fascinated by these giant creatures, often sharing images and theories about what their existence might tell us about Earth’s history.
The intrigue surrounding giant insects continues, and while oxygen played a role, it’s clear that the story is more complex than once thought.
