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Why are insects considered the largest class of arthropods?

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Illustration showing a variety of adult insects, each labeled with its common name and order, including walkingstick, earwig, stonefly, tree cricket, dragonfly, female scale, cat flea, thrips, sucking louse, thysanuran, ant, scarab beetle, stinkbug, mosquito, and cabbage butterfly, highlighting their diverse shapes and sizes. — insect An illustration of insect diversity.

Insects are considered the most successful and largest class of arthropods primarily due to their immense diversity and adaptability. With approximately 1 million described species, insects account for about three-fourths of all known animal species, though estimates suggest the actual number could reach 5 to 10 million.12

Several key factors contribute to this dominance:

Adaptability: Insects have successfully colonized nearly every terrestrial and freshwater habitat on Earth, ranging from deserts and jungles to glacial fields and hot springs.3
Biological Advantages: Their success is linked to their small size, high reproductive rates, and the widespread availability of food sources.3
Coevolution: The evolution of insects has closely paralleled that of flowering plants, leading to specialized feeding methods and mutualistic relationships that have fueled further diversification.4
Ecological Impact: Insects dominate present-day land fauna, playing critical roles in ecosystems such as pollination and nutrient cycling.14

While arthropods as a whole represent about 84 percent of all described animal species, insects constitute the vast majority of this group.2