Prehistoric Insect Size Comparison
One of the most difficult things to appreciate about prehistoric insects is their size. We are accustomed to insects being small — most modern insects are well under 10 cm in any dimension. But in the Carboniferous and Permian periods, some insects reached sizes that seem almost impossible by modern standards.
Size References
Meganeura monyi — Wingspan: ~65-70 cm. Roughly the wingspan of a modern crow.
Arthropleura — Length: up to 2.6 m. Longer than most adult humans are tall. Wider than a car tire.
Titanoptera (largest species) — Wingspan: ~30-40 cm. Comparable to a modern pigeon in wingspan.
Kalligrammatidae (largest species) — Wingspan: ~15 cm. Similar to a large modern butterfly like a Queen Alexandra's birdwing.
Palaeontinidae — Wingspan: ~15 cm. About three times the size of the largest modern cicadas.
Largest modern insect (by wingspan) — The white witch moth (Thysania agrippina) can reach wingspans of about 30 cm, making it comparable to a mid-sized Titanopteran. The largest modern dragonfly is Megaloprepus caerulatus with a wingspan of about 19 cm — less than a third of Meganeura's.
Why Size Matters
The enormous sizes of Carboniferous and Permian insects are not just curiosities. They tell us important things about ancient atmospheric conditions (see Oxygen and Gigantism), ecological relationships (what was a predator, what was prey), and the constraints that have shaped insect body plans for the past 300 million years. The fact that insects never returned to Carboniferous sizes, even when oxygen levels rose again later, suggests that other factors — particularly competition with flying vertebrates — now impose upper limits on insect body size.