More than 1,500 listings of live animals for sale have been found on Facebook in Thailand by a wildlife trafficking watchdog.
Traffic, which monitors such activity, said many of the species, despite having international protection, were not native to the country, and so trading them was unregulated.
The listings were found on 12 Facebook groups during one month in 2016.
Facebook said it did not allow the trade of endangered species.
Among the 200 different species listed for sale were two non-native species banned from international commercial trade – the Eurasian otter and the black spotted turtle.
Some of the animals for sale which are banned from international commercial trade are native to Thailand, such as the helmeted hornbill – which is critically endangered – the Siamese crocodile and the Asiatic black bear.
Traffic analysed membership of the Facebook groups two years later and found that, while two groups had ceased to exist, total membership had almost doubled – up from 106,111 in 2016 to 203,445 in 2018.
The adverts included live and dead animals, as well as animal parts in some cases.
Thailand’s wildlife protection laws did not prohibit the sale of 47% of the advertised species – this was sometimes the case with non-native species.
There were 105 species for sale despite protections under Thai law.
“Growing online wildlife trade will only pile further pressure on threatened non-native species that currently have no legal protection or regulation,” said Kanitha Krishnasamy, Traffic’s acting regional director in south-east Asia.
A spokeswoman for Facebook said: “Facebook does not allow the sale or trade of endangered species or their parts, and we remove this material as soon as we are aware of it.
“We are committed to working with Traffic and law enforcement authorities to help tackle the illegal online trade of wildlife in Thailand.”