One of the many mutant opponents that the movie monster Godzilla contends with is Mothra, a giant mothlike creature with a wingspan of 7–8 m. Science fiction creatures like these can be critiqued on the grounds of biomechanical and physiological principles. Focusing on the principles of gas exchange that you learned about in this chapter, what problems would Mothra face? Why do you think truly giant insects are improbable?

Verified step by step guidance

1. Understand the principles of gas exchange in insects: Insects breathe through a system of tubes called tracheae, which directly deliver oxygen to tissues and remove carbon dioxide. This system works well for small organisms but becomes inefficient as body size increases.
2. Consider the scaling of the tracheal system: As the size of an insect increases, the volume of its body grows faster than the surface area of the tracheae. This means that larger insects would need disproportionately larger tracheae to supply enough oxygen to their tissues, which could be structurally impractical.
3. Analyze the impact of increased body size on oxygen diffusion: The diffusion of gases through the tracheal system is effective over small distances but becomes less efficient over longer distances. In a giant insect like Mothra, the distance for oxygen to diffuse would be much greater, potentially leading to inadequate oxygen supply to cells far from the tracheal openings.
4. Evaluate the mechanical limitations: The exoskeleton of insects must be shed and regrown through a process called molting. Supporting a massive exoskeleton and the physical process of molting would be challenging for a giant insect due to the increased weight and the strength of materials required.
5. Reflect on evolutionary feasibility: From an evolutionary perspective, the constraints on respiratory efficiency, structural support, and other physiological factors make it improbable for insects to evolve into very large sizes under current Earth-like conditions.