The most abundant group of organisms in the animal kingdom?

Analyze the question: It asks which group has the greatest number of organisms (and species) in the animal kingdom.

Explain the concept: The animal kingdom is divided into phyla, and those into classes. The largest phylum is Arthropoda, and its biggest class is Insecta. Insects make up more than half of all known animal species, with over a million described species and possibly millions more yet to be discovered.

Compare the options:

• A. Mammalia: about 6,500 species. This is a small class, and it includes humans, goats and cattle.
• B. Aves (birds): about 10,000 species. This is also small by comparison.
• C. Insecta: over 1,000,000 described species, such as grasshoppers, ants, bees, mosquitoes, butterflies and cockroaches. They live in almost every habitat on land and in fresh water.
• D. Annelida: about 17,000 species, such as earthworms and leeches. It is a modest-sized phylum.

Answer: Insecta is by far the most abundant group, so the correct option is C.

Why insects are so successful:

• They are small, so they need little food and space.
• They can fly, which helps them escape enemies and find food.
• They have a waterproof exoskeleton of chitin, which prevents water loss.
• They reproduce quickly and in large numbers.
• They show metamorphosis, so larvae and adults do not compete for the same food.

Exam tip: Remember "Arthropoda is the biggest phylum, and Insecta is its biggest class." If a JAMB question asks about the "largest" or "most abundant" group, think of insects first.