Insects – The Most Successful Animals on Earth | Animal Taxonomy

🐛 Insects – The Most Successful Animals on Earth

By almost any measure, insects are the most successful animals that have ever lived. Class Insecta contains over 1 million described species — more than all other animal groups combined — and estimates of total species including undescribed ones range from 5 to 10 million. Insects have been flying the skies for 400 million years, survived all five mass extinctions, and colonised every terrestrial and freshwater habitat on Earth (only the open ocean remains largely insect-free). They pollinate 75% of the world's flowering plants, decompose organic matter, aerate soils, and underpin nearly every terrestrial food web. Without insects, most ecosystems on Earth would collapse.

The Western Honey Bee (Apis mellifera) — arguably the most economically important insect on Earth, responsible for pollinating crops worth over $200 billion annually. (Wikimedia Commons)

🧬 What Defines an Insect?

All insects share a common body plan: three body segments (head, thorax, abdomen), six legs (three pairs, attached to the thorax), one pair of antennae, and most have one or two pairs of wings. Their exoskeleton is made of chitin — rigid, lightweight, and impermeable to water. Most insects undergo metamorphosis: either complete metamorphosis (holometaboly: egg → larva → pupa → adult, as in butterflies and beetles) or incomplete metamorphosis (hemimetaboly: egg → nymph → adult, as in grasshoppers and dragonflies).

🐞 The Major Insect Orders

Coleoptera (beetles) is the largest order with ~400,000 described species — famously prompting the quip attributed to J.B.S. Haldane that God has “an inordinate fondness for beetles.” Diptera (true flies, mosquitoes, gnats) includes the mosquito — responsible for more human deaths than any other animal through malaria, dengue, and Zika. Hymenoptera (ants, bees, wasps) are the master social insects, with ant colonies of up to 700 million individuals; ants alone comprise ~20% of total terrestrial animal biomass. Lepidoptera (butterflies and moths) encompasses ~180,000 species. Orthoptera (grasshoppers, crickets, locusts) includes locusts capable of forming swarms covering hundreds of km². Odonata (dragonflies, damselflies) are among the oldest winged insects, appearing ~325 million years ago; Meganeura, a Carboniferous dragonfly ancestor, had a 70cm wingspan.

📌 Key Facts & Milestones

• ~400 million years ago — First insects evolve on land (Devonian)
• ~325 million years ago — First flying insects appear; Meganeura with 70cm wingspan
• 1 million+ — Described insect species; estimated 5–10 million total
• 10 quintillion — Estimated total number of individual insects alive at any time
• Honey bee — Pollinates crops worth $200+ billion annually
• Goliath beetle — Heaviest insect (up to 100g); Atlas moth — Largest wingspan (up to 30cm)

🎥 Watch: The World of Insects

Beetles, butterflies, bees, ants, and mosquitoes — why insects are the most successful class of animals that has ever evolved.