Why were prehistoric insects so huge?


Poster for the film The Deadly Mantis (1957) by artist Reynold Brown, via Wikimedia Commons. Okay, prehistoric insects weren’t this big, but many were much larger than insects today.

Do you complain about dead bugs on your windshield? Then be thankful that insects today are smaller than their prehistoric ancestors.
Hundreds of millions of years ago, giant insects were common on Earth. Consider Meganeura, a genus of extinct insects from approximately 300 million years ago, related to modern-day dragonflies. One member of this group – M. permiana – was first described by researchers in Kansas in 1937 as having a wingspan of over 2 feet (0.6 meters). It’s still considered one of the largest known insects that ever lived.
While over a million insect species live today, truly giant insects no longer exist. Why did they disappear?