When Insects Were Huge?

Insects reached their biggest sizes about 300 million years ago during the late Carboniferous and early Permian periods. This was the reign of the predatory griffinflies, giant dragonfly-like insects with wingspans of up to 28 inches (70 centimeters).

Why were ancient insects so large?

The leading theory is that ancient bugs got big because they benefited from a surplus of oxygen in Earth's atmosphere. But a new study suggests it's possible to get too much of a good thing: Young insects had to grow larger to avoid oxygen poisoning.

What was the largest insect that ever lived?

With wingspans that could reach 27 inches, the largest known insects of all time are griffinflies from the genus Meganeuropsis, Clapham says via email. The largest of their fossils were found in France and Kansas and were 300 million to 280 million years old.