Beetles are the most diverse group of insects. Their order, Coleoptera (meaning "sheathed wing"), has more described species in it than in any other order in the animal kingdom. Forty percent of all described insect species are beetles (about 350,000 species), and new species are regularly discovered. Estimates put the total number of species, described and undescribed, at between 5 and 8 million.

​

Beetles can be found in almost all habitats, but are not known to occur in the sea or in the polar regions. They impact the ecosystem in several ways. On one hand, they feed on plants and fungi, break down animal and plant debris, and eat other invertebrates. On the other hand, they are prey of various animals including birds and mammals.

​

Certain species are agricultural pests, such as the red flour beetle Tribolium castaneum, the Colorado potato beetle Leptinotarsa decemlineata, or the mungbean beetle Callosobruchus maculatus Fabr, while others are important controls of agricultural pests. For example, lady beetles consume aphids, scale insects, thrips, and other plant-sucking insects that damage crops.