Terrestrial animal

Terrestrial animals are animals that live predominantly or entirely on land (e.g. cats, chickens, ants, most spiders), as compared with aquatic animals (e.g. fish, whales, octopuses, lobsters, etc.), who live predominantly or entirely in bodies of water; and semiaquatic animals (e.g.crocodilians, seals, platypus and most amphibians), who inhabit coastal, riparian or wetland areas and rely on both aquatic and terrestrial habitats. While most insects (who constitute over half of all known species in the animal kingdom) are terrestrial, some groups, such as mosquitoes and dragonflies, spend their egg and larval stages in water but emerge as fully terrestrial adults after completing metamorphosis.

In a narrower sense, the word "terrestrial" is used to specifically describe animals that live on the ground (particularly those living obligately on the soil surface), as opposed to arboreal animals that live in trees, even though trees, like the shrubs and groundcovers from the lower layers, are all an integral component of the terrestrial ecosystem.

The term "terrestrial", in a more specific sense, is typically applied to species that live primarily on the ground or in burrows inside the soil, in contrast to arboreal species, who live primarily in trees, even though the latter are actually a specialized subgroup of the terrestrial fauna.

There are other less common terms that apply to specific subgroups of terrestrial animals:

Terrestrial invasion is one of the most important events in the history of life. Terrestrial lineages evolved in several animal phyla, among which arthropods, vertebrates and mollusks are representatives of more successful groups of terrestrial animals.

Terrestrial animals do not form a unified clade; rather, they are a polyphyletic group that share only the fact that they live on land. The transition from an aquatic to terrestrial life by various groups of animals has occurred independently and successfully many times. Most terrestrial lineages originated under a mild or tropical climate during the Paleozoic and Mesozoic, whereas few animals became fully terrestrial during the Cenozoic.

If internal parasites are excluded, eleven phyla include free living species in terrestrial environments. These can be grouped as follows:

Three phyla contain species that have adapted totally to dry terrestrial environments, and which have no aquatic phase in their life cycles: