Prehistoric insects were big. If we lived among the giant insects of the Paleozoic era, it would take something bigger than a sneaker to squish a six-legged home intruder. Some of these giant insects, known only from the fossil record, were measured in feet rather than inches. What is the largest insect that ever lived, the species that dwarfed all others in prehistoric times?
The current record holder for the largest insect that ever lived is an ancient griffenfly. Meganeuropsis permiana measured an impressive 71 cm from wing tip to wing tip, a full 28 inch wing span. This giant invertebrate predator inhabited what is now the central U.S. during the Permian period. Fossils of the species were discovered in Elmo, Kansas and Midco, Oklahoma. In some references, it is called Meganeuropsis americana.
Meganeuropsis permiana is one of the prehistoric insects referred to as giant dragonflies. David Grimaldi, in his hefty volume Evolution of the Insects, notes this is a misnomer. Modern day odonates are only distantly related to the giants known as prodonata.
Giant insects like Meganeuropsis permiana lived in the hyperoxic environment of the late Paleozoic era. As the concentration of oxygen in the atmosphere diminished over geologic time, insects became necessarily smaller because of the limitations of their respiratory systems.