The Age of Giant Insects

Key Concepts and Discoveries:

• Population of Insects: There are approximately 10 quintillion insects compared to over 7 billion humans.
• Giant Insects: During the Carboniferous Period (298 to 358 million years ago), insects and arthropods were significantly larger than today. Notable examples include:
  • Meganeura: A griffinfly with a wingspan of about 70 cm, comparable to a pigeon.
  • Stephanotypus: Another griffinfly measuring around 40 cm across.
  • Arthropleura: A giant millipede-like arthropod that could grow to about 2 meters long and half a meter wide.

Factors Contributing to Size:

• Oxygen Levels: The atmosphere during the Carboniferous contained nearly 35% oxygen, allowing for larger body sizes in arthropods.
• Plant Growth: The period was marked by extensive plant growth, which increased oxygen production and decreased carbon dioxide levels due to the absence of wood-decomposing bacteria.

Breathing Mechanism of Arthropods:

Arthropods breathe through spiracles and a network of tracheae, which limits their size based on oxygen availability.

Research Insights:

• Laboratory Experiments: Researchers at Arizona State University found that raising modern insects in oxygen-rich environments led to larger sizes over generations.
• Larval Size Theory: Scientists at Michigan State proposed that ancient arthropods may have evolved larger larvae to mitigate the risk of oxygen toxicity, resulting in larger adult sizes.

Decline of Giant Arthropods:

By the Permian Period (around 275 million years ago), atmospheric oxygen levels began to drop due to climate changes and the emergence of decomposers, leading to the extinction of these giant arthropods.

Conclusion:

The Carboniferous Period is identified as the true "Age of Insects," characterized by the dominance and remarkable size of arthropods, a status that has shifted but still sees insects outnumbering humans significantly today.

Featured Researchers/Sources:

• Arizona State University (research on modern insects)
• Michigan State University (larval size theory)
• Professor Stuart Sutherland (The Great Courses Plus)