JAKARTA — In the market for a new pet? Maybe something a bit exotic? For many consumers, reptiles and amphibians are just the thing: geckos, monitors, pythons, tree frogs, boas, turtles and many more species are available in seemingly endless varieties, many brilliantly colored, some exceedingly rare.

Exotic reptiles and amphibians began surging in popularity in the early 1990s, not only in the United States but also in Europe and Japan. From 2004 to 2014, the European Union imported nearly 21 million of these animals; an estimated 4.7 million households in the United States owned at least one reptile in 2016.

But popularity has spawned an enormous illegal trade, conservationists say. Many reptiles sold as pets are said to have been bred in captivity, and sales of those animals are legal. In fact, many — perhaps most, depending on the species — were illegally captured in the wild.

“It’s the scale that matters, and the scale is huge, much bigger than people realize,” said Vincent Nijman, an anthropologist at Oxford Brookes University in England.