In contrast with the endemic species, foreign lizards are “invasive” species that are not naturally evolved or geographically segregated in Taiwan , but rather were introduced by humans, either deliberately or inadvertently, and have adapted to the environment of Taiwan and formed stable breeding populations. The most prominent example is the green iguana. This species of lizard is often hunted for food in foreign countries, and its numbers are dwindling to the point of extinction. The bright coloration of a juvenile green iguana makes it a popular pet for the public, and was imported in large numbers by Taiwan 's pet merchants. In the days of inadequate conservation-related laws, these now-protected lizards were imported illegally by unlawful merchants, hoping to make profits by selling to lizard fans in Taiwan . However, as these animals mature, they grow huge and become hard to maintain, requiring lots of space and monetary efforts. They could even become dangerous if they become too big. Lizard fans with a conscience will seek help from relevant organizations by donating to conservation agencies or museums for research; however, those who do not (sadly, the majority) will irresponsibly abandon them in the wild. Usually, a foreign species will not survive easily in a foreign environment, requiring specialized equipment (aquariums, incubators, etc) to regulate its temperature and humidity, in order to stay alive. They will most like perish if left in the wild. However, green iguanas were able to adapt quickly to Taiwan 's environment once they were abandoned, and quickly formed stable breeding populations, threatening the stability of local species. This is resulted in a strange phenomenon: a protected species that is invasive in Taiwan .

The earliest record of the foreign lizard species in Taiwan was the Common Sun Skink ( Eutropis multifasciata ), first discovered in Kaohsiung County in 1992. These lizards were thought to have been accidentally introduced together with the importation of logs from the Indonesian island of Java . A more recent record was the Brown Anole ( Anolis sagrei ) found in the nursery patches of Sanjiepu, Chiayi County . These lizards are native to Cuba , the Bahamas and nearby islands in the Caribbean , and juveniles were discovered by researchers as early as 1998. In just two years the populations become stable, and an aggressive invasive species was born. However, there seem to be no signs of expansion in its distribution in recent years, although its effects on the local lizard species (especially the Agamidae ) have yet to be studied thoroughly.

Whether or not a pet animal like the green iguana can be considered foreign is still highly debated. After all, it may be too early to call any protected species foreign, whether they are imported for pets or smuggled illegally from abroad. Regardless, the invasion by these foreign species will certainly threaten the local species, especially those that are endemic to Taiwan . How to control the influence of these animals on the environments is an issue that needs to be addressed quickly.