Why the world's largest insects were hunted into submission

Nature · Published 21 October 2026 Swipe more like this →

In short: 320 million years ago, dragonflies with wings as long as human arms and centipedes the size of people dominated the Earth. Today, they are gone. For decades, we blamed the atmosphere for their demise, but a new discovery suggests they were actually hunted into extinction by the rise of birds.

For over a century, the prevailing theory held that atmospheric oxygen dictated insect size. Because insects lack lungs and bloodstreams, they rely on microscopic holes in their bodies to oxygenate their tissues. Scientists believed that during the Carboniferous and Permian periods, oxygen levels were significantly higher—reaching over 30 percent compared to roughly 20 percent today. This high concentration allowed insects to fuel faster metabolisms and larger bodies, leading to behemoths like the Meganeura dragonfly and the Arthropleura centipede.

However, recent data analysis of over 10,500 fossilized insect wings by researchers Matthew Clapham and Jereder Karr has complicated this narrative. Insect wingspan sizes mirrored oxygen concentrations throughout their initial 150 million years of development, yet this link ceased during the early Cretaceous, specifically between 140 and 130 million years ago. During this window, even as oxygen levels began to climb from a Jurassic low of 15 percent, insects actually began to shrink.

The culprit appears to be a biological shift rather than a chemical one: the evolution of birds. By the early Cretaceous, feathered flying dinosaurs had developed specialized features like the alula—a thumb-like wing projection that allowed for precise maneuvering at low speeds. These birds exerted a "size-selective pressure" on the insect population. While small insects remained too agile to catch, the larger individuals became easy prey. By systematically removing the giants, birds prevented the species from ever reaching their former prehistoric scales again.

General information, not professional advice. Spotted an error? Flag the card or see corrections and complaints.

Intellect Plus is a visual educational discovery platform for exploring fascinating facts and ideas. Brain Food, Not Brain Rot. What is Intellect Plus?

Related

• Why did the dragonflies of the Carboniferous period eventually vanish?
• Why prehistoric dragonflies grew to the size of modern seagulls
• Why prehistoric insects grew to terrifying sizes
• Was the giant prehistoric insect Meganeura actually a victim of its own massive size?
• Why insects once ruled the Earth as true giants of the Carboniferous period.
• Witness the hidden lives of nature's smallest hunters and survivors
• Your backyard milkweed might be trapping monarch butterflies in a deadly, parasitic cycle
• The ultimate success story: why Earth cannot function without insects
• Why this tiny bee endures a punch to the face for your ice cream
• The Amazonian Treehoppers Use Vibration to Call for Help
• A cameraman faces a swarm of hornets while continuing to film the encounter.
• Why these aquatic predators spend their entire lives swimming upside down in the water

More in Insects · More in Nature · Latest · A–Z · All topics