Although most humans probably do not lament the disappearance of dog-sized insects, a handful of scientists do. These scientists obviously don’t watch the same movies we do. Recently, a group of researchers from Argonne National Laboratory’s Advanced Photon Source along with some other researchers from less badass sounding institutions used advanced x-ray equipment to try to determine why giant insects don’t roam the earth devouring amorous teenage couples today.
X-ray imaging of beetles helps confirm that tracheal system design may limit size in insects.
The answer lies in their primitive respiratory systems. Unlike vertebrates in which oxygen is transported via the lungs to the blood and then throughout the body, insects transport oxygen via a network of blind-ending tracheal tubes. Pathetic! By examining different sized beetles, the scientists discovered that as the size of a beetle increases, the size of the tracheal tubes required to keep the bug going with a good O2 buzz increases disproportionately. This means that the larger the insect, the less room there is for other organs as tracheal tubes crowd everything else out.
In the late Paleozoic Era, when monster bugs were all the rage, oxygen levels were at record highs. As oxygen levels decreased, however, the cuddly teddy bear-sized insects disappeared as well. Perhaps not coincidentally, this subsequent period also gave rise to the picnic.