Prehistoric Atmospheric Conditions

One of the key factors allowing insects to reach such gargantuan proportions was the elevated atmospheric oxygen of the late Carboniferous period (approximately 318–299 million years ago):

• Oxygen Levels: Estimates suggest 30–35 % O₂, compared to today’s ~21 %.
• Respiratory Constraints: Insects rely on passive diffusion of oxygen through their tracheal systems. Higher ambient O₂ meant oxygen could diffuse further into tissues, supporting larger body sizes.
• Dense Vegetation & Humidity: Vast coal-forming swamps with abundant plant life created moist, oxygen-rich microhabitats—optimal for giant insect growth.

While today’s largest insects top out around 19 cm (the Giant Weta or the Atlas moth), nothing quite matches the sheer enormity of Meganeura. Elevated Carboniferous oxygen levels and humid swamp ecosystems enabled these prehistoric flyers to flourish. Although such giants no longer roam our skies, studying them offers fascinating insights into how Earth’s changing atmosphere shapes the limits of animal size.

The Giant Weta (Genus: Deinacrida)

The Giant Weta comprises several species of large, flightless crickets endemic to New Zealand. Some individuals can weigh up to 71 g, making them among the heaviest insects alive today.

The Atlas Moth (Attacus atlas)

The Atlas moth is one of the world’s largest moths by wing surface area, renowned for its spectacular wing patterns that mimic snake heads.

From the weighty, ground-dwelling Giant Weta of New Zealand to the ethereal Atlas moth drifting through Asian rainforests, these modern giants remind us of the incredible diversity and adaptability of insects. Though vastly different from the Carboniferous behemoths like Meganeura, they each hold record-breaking titles today and play vital roles in their ecosystems.