giant insects of the carboniferous
28 July 2008
The Carboniferous period gets its name from the vast deposits of coal it left behind. This coal had to come from somewhere, and it did: from the enormous swamps that covered the supercontinent Pangaea, which formed over the course of the Carboniferous. These swamps were full of the most primitive land plants, like horsetails, ferns, and lycopods, but grown to a massive size in the oxygen-rich environment they created.

Estimates have placed the atmospheric oxygen content during the Carboniferous at as high as 35% (oxygen currently makes up 21% of the atmosphere). Scientists believe that this high oxygen content not only allowed plants to attain incredible stature; it also facilitated the existence of other gigantic organisms, including the dragonfly
Meganeura, whose wingspan was seventy centimeters (two and a half feet).

Many different species of gigantic dragonfly existed during this period, as well as gargantuan versions of our modern mayfly and, of course, cockroach. Scientists believe that high oxygen levels compensated for the inefficiency of the insects’ respiratory systems, which, unlike humans’, are not centralized and rely on the passive diffusion of air through their tissues. In the lower-oxygen-content atmosphere of today, insects’ respiration is too inefficient to allow their bodies to grow much thicker than (in the dragonfly’s case) a pencil, and indeed, giant insects began to disappear as the Permian period dawned and oxygen levels began to decline.