The fauna of West Virginia include all those animals typically identified as wild. Those animals that have been domesticated and kept in captivity, such as dogs, cats, horses, cattle, sheep, goats, and pigs, are usually not included.

There are two basic groups, vertebrates and invertebrates. The vertebrates have a backbone, a bony internal skeleton, and limbs (legs or wings or fins) that are supported by several specialized bones. Vertebrates include mammals such as bear, deer, squirrels, rabbits, and bats; birds such as ducks, geese, grouse, turkey, hawks, eagles, robins, and hummingbirds; reptiles such as lizards, snakes, and turtles; amphibians such as salamanders, frogs, and toads; and fish such as bass, trout, catfish, carp, shiners, and bluegill.

In contrast, the invertebrates do not have a bony internal skeleton. Some have a hard outer skeleton (an exoskeleton) that supports their body shape, but have no bony structures within their bodies. Butterflies, bees, grasshoppers, crayfish, clams, snails, and spiders are some of the common invertebrate fauna with an exoskeleton. Other invertebrate fauna, such as earthworms, flatworms, and tapeworms, lack both an internal skeleton and an outer exoskeleton.

There are six major faunal groups present in West Virginia: (1) flatworms (planaria, flukes, and flatworms); (2) roundworms (hookworms and heartworms); (3) annelids (earthworms); (4) arthropods (insects, centipedes, millipedes, spiders, ticks, mites, and crayfish); (5) mollusks (snails, slugs, clams, and mussels); and (6) vertebrates (mammals, birds, reptiles, amphibians, and fish).

Biologists have reliable estimates of the numbers of different kinds of vertebrates that live in West Virginia: 74 species of mammals, 354 birds, 61 reptiles, 28 amphibians, and 182 fish. Invertebrates have not been nearly so well studied. Surveys indicate there are 35 species of mosquitoes, 30 species of crayfish, 68 species of horse flies and deer flies, 43 species of stoneflies, 49 species of mayflies, 135 species of butterflies, 176 species of caddisflies, 58 species of mussels (clams), 200 species of damselflies and dragonflies, more than 500 species of spiders, and more than 700 species of macromoths in West Virginia. Due to the small size, secretive behavior, and difficulties of identification of many other invertebrate groups, biologists have not been able to estimate their numbers. Certainly, the numbers of species of invertebrates greatly exceed the numbers of species of vertebrates. Likewise, the total number of individual invertebrates greatly exceeds the total number of individual vertebrates. The total number of species of West Virginia fauna probably exceeds 10,000.

West Virginia animals are quite diversified, due to the variety of habitats. Climate, geology, soils, and topography have combined in West Virginia to produce distinct plant communities. This diversity of plant communities is directly responsible for the diversity of the state's fauna. Every county and every habitat support a wide variety of animals.

West Virginia animals range in size from more than 500 pounds for the black bear to the countless microscopic invertebrate forms. They occur in the soil, in the water, in grass, and in trees. They run, jump, swim, crawl, burrow, and fly. Some have more than one mode of travel. Most are dependent on specific plant communities to provide their food, water, and shelter. Others are parasites and live on the inside or outside of other fauna. While some are nocturnal, others are diurnal.

Certain animals are specialists and occur only in specific habitats in specific regions of West Virginia. Several species (such as fish) are restricted to water. Cool mountain streams suffice for brook trout, while the slow-moving, warm rivers are ideal habitat for carp and catfish. Cave species are among the most specialized of all West Virginia fauna. Such groups as the cave crickets, cave crayfish, and cave salamanders spend their entire lives in darkness. Some beetles, such as the cobblestone tiger beetle, exist only on the gravel bars along islands in the Ohio River. The West Virginia northern flying squirrel and the Cheat Mountain salamander are restricted to the red spruce forests above 3,000 feet, while the northern water shrew is restricted to swiftly flowing, rocky-bedded streams at higher elevations.

Many other faunal species are generalists and live in almost every habitat in every county of West Virginia. Examples are the white-tailed deer, gray squirrel, cottontail rabbit, blue jay, cardinal, robin, spring peeper, American toad, box turtle, largemouth bass, bluegill, black bullhead, eastern tiger swallowtail, and silver-spotted skipper.

A few of the fauna are endemic to West Virginia, meaning they are found nowhere else. The best-known examples are the Cheat Mountain salamander and the West Virginia spring salamander.

Most West Virginia animals are resident species, spending their entire lifetime within our state's boundaries. All fish, amphibians, and reptiles, and most mammals (with the possible exception of a few bats), are year-round residents. All invertebrates, with the exception of a few species of butterflies such as the Monarch, are also year-round residents. Other animals are seasonal visitors, spending part of the year in West Virginia and migrating to some other area for the remainder of the year. Birds are the most obvious seasonal visitors. Some, such as the warblers, nest in West Virginia during summer months but migrate to Central America for the winter. Others, including waterfowl, pass through West Virginia while migrating between wintering grounds in southern coastal states and nesting grounds in Canada. A rare few, such as the rough-legged hawk that nests in Canada, are present in West Virginia only during winter months.

The last great change to affect West Virginia fauna was the Ice Age of Pleistocene times, approximately 10,000 B.C. Although glaciers never reached the region that is now West Virginia, there was permanent snow cover over much of the present state during most of the year. Tundra vegetation, and later northern boreal vegetation, dominated this region, with such species as balsam fir and red spruce covering much of the area, extending from mountaintops to river bottoms. Many northern species of animals occupied West Virginia during that long period of continual winter. But, as the climate warmed and the great ice sheets melted and receded northward, a retreat of northern plants and animals took place. The climate in the river valleys and other lowlands was too warm for northern species, and only those at the highest elevations, 4,000 to 5,000 feet, survived. At these heights, the climate remained suitable for northern species such as the northern flying squirrel, snowshoe hare, and Cheat Mountain salamander. These are some of the northern fauna that today are considered to be relicts of the Ice Age.

The West Virginia fauna are again faced with a changing environment, this time due to humans, not to natural climate changes. Land-use practices during the past 200 years resulted in many changes to our state's fauna. Some species disappeared from West Virginia, while new species appeared. The clearing of lands by early settlers to create farms had both negative and positive impacts on our native animals. The passenger pigeon, timber wolf, bison, and elk disappeared. The mountain lion, beaver, river otter, and golden eagle were greatly reduced. In contrast, the bobwhite quail, barn owl, and opossum quickly adapted to these new habitats, and their numbers increased.

At the same time that some of the native fauna were being reduced, new animals became established in the Mountain State. Some were introduced intentionally and others accidentally. Some of the exotic fauna that are present throughout much of the state today include the English sparrow, European starling, carp, brown trout, rainbow trout, gypsy moth, honey bee, and zebra mussel.

Many developments impacted our fauna during the past 100 years, including logging, pesticides, acid precipitation, and the chestnut blight. One of the most significant was the damming of rivers. West Virginia has no natural lakes, apart from one small pond, thus those fauna that required deep lake waters typically did not exist here. As dams were constructed on the Ohio River and on the Bluestone, Cheat, Elk, Gauley, Guyandotte, Little Kanawha, Tygart, and West Fork rivers, vast acreages of new habitat were created. Birds, such as bald eagles, Canada geese, and cormorants, are the most obvious fauna that have been attracted to this new habitat.

The West Virginia fauna of today are a mix of four distinct groups: (1) native species that are similar to those that occupied the mountains before European-American settlement; (2) exotic species that were accidentally or intentionally introduced by humans; (3) species that have naturally invaded from the south and occupy the lower southern river bottoms, and (4) relict species from the last Ice Age that occupy the higher elevations.