Since Jeju Island is located at the southern most part of Korea, even the same species are categorized as subspecies due to the distance they live apart from each other. This phenomenon is attributable to unique circumstances of long isolation from the mainland.
A geographical picture shows Japan at the East, China at the West, Taiwan at the South, and the Korean Peninsula at the North of Jeju. Seasonal transformations of migratory birds and insects have been detected conspicuously. Restricted numbers of amphibian reptiles and mammals, which lack migratory habits, have been transformed as well.

Insects

The first announcement of insects of Jeju Island to the academic world was made by Tatum (1847) in the "Description of New Species of Carabus from Asia" in the Ann. Mag Nat. Hist 20:14-15. In it, the Jeju ground beetle. Carabus monilifer (Same type but of a different name from Carabus smaragdinus monilifer Tatum), of ground beetle order ground beetle family, was reported to our academic world for the first time.
Distinctive insects in Jeju island are comprised of 23 subtropical zone types, 47 frigid zone types, and 19 indigenous insects.

Amphibians / Reptiles

Amphibians and Reptiles of Jeju Island are the same as those of the mainland. However, it is located in the extreme southern area and there are many types of animals that live in this island since it is located between the Korea mainland, Japan and China.
Amphibians confirmed by documentations and site surveys are comprised of 4 orders and 5 families, and reptiles of 4 orders and 8 species (Table 5). Sibynophis chinensis is one type of reptile that inhabits Jeju. Scinella laterale laterale, coluber spinalis, takydromus wolteri and amphiesma vibakari ruthveni are being reduced in other regions but these inhabit Jeju Island more than other place. Observed and reported types in Jeju are made up of 2 orders, 5 families and 9 species of Amphibia and 1 order, 5 families, and 12 species of Reptiles.
Exterminated and conservative wild animals designated by the Ministry of Environment was not confirmed but Amphibia and Reptiles are being reduced and to be conserved due to environmental pollution and indiscriminate hunting. 
 

Birds in the Korean Peninsula

394 species of birds, 430 including subspecies, are reported to live in the Korean Peninsula. Among 373 species except stray birds, 100 species are known to be resident birds and 273 species are reported to be migratory birds.
290 species, with 61 species of passing migratory birds, 90 winter migratory birds, 41 resident birds, 50 summer birds, and 48 stragglers are detected in Jeju Island. Due to the geographical position of Jeju Island, it has accommodated more winter migratory and passing birds, compared to other areas in the Korean Peninsula. Birds in Jeju Island account for 73.6% of those in entire the Korean Peninsula.

Mammals

There are about 4,000 species of mammals living on earth, with 87 species in Korea. Among them, 5 orders, 8 families, 23 species (including 4 subspecies) of mammals live in Jeju Island. Rare species of mammals, such as brown bears, boars, deer, and roe deer had left their traces in fossil beds, which indicates a geographical isolation of the island and the insufficient terrains for mammals to live.
Indiscriminate hunting of Japanese military forces during the colonial period and government forces at the time of the April 3rd grass-roots riots reduced the number of mammals drastically.
Abuse of agricultural chemicals has recently destroyed the animal food chain. Rapid urbanization of also serves to restrict the natural habitat for animals, which leads to a drastic decrease of wild animals. Some species of mammals that are decreasing in numbers are the Jeju Weasel, and badgers that need special protection for their survival. The Lynx is assumed to be near extinction. Among them, the number of roe deer is increasing.