Which class has more species than all other animal phyla combined?

• A. Insecta
• B. Arachnida
• C. Crustacea
• D. Myriapoda

Answer: (A)

Insects are the most species-rich class, with far more described species than all other animal phyla combined. This immense diversity comes from a combination of traits and evolutionary opportunities: flight enables wide dispersal and occupation of many habitats; metamorphosis creates separate life stages specialized for different resources, reducing competition between larvae and adults; a vast array of mouthparts and dietary strategies allows insects to exploit nearly every plant and animal niche; their small size and short generation times promote rapid evolution and speciation; and their dependence on plants and microhabitats has driven extensive diversification across many ecosystems. While groups like arachnids, crustaceans, and myriapods are diverse, their total species counts are far smaller than that of insects.