Whole species disappear from the wild as millions of animals are illegally exported round the world in a business with profit margins that rival the drugs trade

Countries across south-east Asia are being systematically drained of wildlife to meet a booming demand for exotic pets in Europe and Japan and traditional medicine in China – posing a greater threat to many species than habitat loss or global warming.

More than 35 million animals were legally exported from the region over the past decade, official figures show, and hundreds of millions more could have been taken illegally. Almost half of those traded were seahorses and more than 17 million were reptiles. About 1 million birds and 400,000 mammals were traded, along with 18 million pieces of coral.

The situation is so serious that experts have invented a new term – empty forest syndrome – to describe the gaping holes in biodiversity left behind.

"There's lots of forest where there are just no big animals left," says Chris Shepherd of Traffic, the wildlife trade monitoring network. "There are some forests where you don't even hear birds."

Seahorses, butterflies, turtles, lizards, snakes, macaques, birds and corals are among the most common species exported from countries such as Malaysia, Indonesia and Vietnam. Much of the business is controlled by criminal gangs, Shepherd says, and many of the animals end up in Europe as pets. The rarer the species, the greater the demand and the higher the price. Collectors will happily pay several thousand pounds for a single live turtle.

Vincent Nijman, a researcher at Oxford Brookes University who has investigated the trade, said: "We see species that are in fashion traded in great numbers until they are wiped out and people can't get them any more. So another one comes in, and then that is wiped out, and then another comes in."

He added: "In Asia, everybody knows the value of wildlife, so people go into the forest and, whatever they encounter, they know it has a value and that there is someone they can sell it to."

Nijman's research offers the first glimpse of the size of this widespread trade. While most people are aware of illegal sales of rhino horn and ivory, he says it is the scale of the movement of lesser-known species that is most disturbing.

He analysed 53,000 records of imports and exports from countries under Cites, the international convention that regulates the sale of wildlife. Most common species are not listed under Cites, so do not appear in the records. Trade in the most endangered, such as rhino and tiger, is banned. Nijman looked at species considered vulnerable enough that trade is allowed, but controlled. "I'm not against the wildlife trade at all. I think it is a very important economic driver for a large part of the region and a lot of people are dependent on it," he said. "But it has to be done in such a way that you don't finish it all this year. It's not like oil, where you drill it out and then it's gone. If you organise and regulate it properly, it should go on for ever."

Cites records between 1998 and 2007 showed that of more than 35 million animals exported during that period, some 30 million were taken from the wild. The EU and Japan were among the most significant importers.

For some mammal species, the proportion sourced from the wild dropped significantly over the decade, and traders were forced to rely increasingly on captive-bred animals. Official trade in birds virtually disappeared by 2007, probably because of bird flu restrictions.

The bulk of seahorses traded were in the form of dried specimens for Chinese medicine. "The moment you look into the wildlife trade in south-east Asia, China is the biggest challenge, because they can use everything and they will use everything."

Trade in the Asian pangolin, a scaly anteater, illustrates the problem. Officially, countries do not allow their commercial sale and agreed a zero quota under Cites in 2000, though regular seizures show widespread trade, for medicine and meat. "The countries closest to China get emptied [of pangolin] first. Vietnam and Laos have been drained. Myanmar has been drained and they are working south, so now Indonesia is being emptied of pangolins," Shepherd says. "Prices are very high and in the next few years we will see pangolins being sucked out of Africa to supply the demand."

Nijman says his analysis of the Cites records, published in the journal Biodiversity and Conservation, inevitably underestimates the scale of the trade. "There is always an unknown quantity of Cites-listed species that are traded without being reported, and on top of that, probably much larger, is the trade in non-Cites species, which are the species that we think are still common enough to be traded without controls."

One of these is the tokay gecko. "Every­one who has been to Indonesia or Malaysia will know them because they are the ones that sit in your hotel room. You have them everywhere." Although not listed by Cites, Indonesia has set a limit of 45,000 of the lizards exported each year as pets. Nijman says the true number traded is much higher, perhaps into the millions. "We can't say whether a million tokay geckos being traded a year, or two million, is too many. Perhaps there are so many it is OK. But you would think that if they set the quota at 45,000 then a million is too much."

Such geckos can be typically bought in rural villages for a few cents each, and sold for $10 – a profit margin that rivals the drugs trade. "It's a great business. No wonder organised crime gets involved and starts running things," Shepherd says. "In Malaysia if you get caught selling drugs you get the death penalty. For wildlife crime the maximum fine is about $5,000."

The situation is acute in south-east Asia, but the trade, both legal and illegal, is global, often using the internet and courier delivery. For $4,000, an illegal trader based in Indonesia will send a three-year-old ploughshare tortoise from Madagascar, one of the most endangered animals in the world.

Other species sell for as much as $20,000, though Nijman and Shepherd do not want to advertise which ones. "People do know about the rhinos and the tigers, but the vast majority of this trade is in stuff that they didn't know existed," said Shepherd. "A handful of people are getting very rich and most people are getting screwed out of their natural resources."