Li began keeping the bugs seven years ago, influenced by the trend in Japan, where raising pet beetles has long been a popular hobby for children and adults alike. He soon became fascinated by the diverse beetle world, which includes up to 350,000 species.

By 2007, Li had so many beetles he couldn't fit them all at home, so he opened a shop to house some of his pets and share his interest with others. It started poorly: he didn't make any sales for the first three weeks.

'People were curious and kept asking questions, but they were hesitant about buying beetles. That's understandable; after all I'm selling unconventional pets,' Li says.

To promote interest in beetles, he created a website (hkbeetle.com) outlining the features and behavioural patterns of various species. It was evidently intriguing enough to help people overcome their initial wariness. Electrical technician Wong Ka-fai says he learned about the pursuit two years ago and was hooked immediately. 'How often can we follow the entire life cycle of an insect?'

The 32-year-old, who owns six pairs of beetles, even bought bugs as gifts for a friend's child. 'It's an interesting way to teach kids about respecting living creatures and how nature works,' he says.

Part of the appeal for enthusiasts such as Wong is the feeling of involvement: most raise their beetles from eggs, waiting months for them to hatch and mature from larvae into adult specimens.

Fourteen-year-old Chia Chin-yan has also become a fan despite objections from her mother and friends. 'They say the beetles are disgusting, but I find them really cute. I often take them out of their glass tank and play with them,' says the schoolgirl, who has two pairs of beetles.

This beetle mania has led to an increase in specialist shops. From just five shops selling insects 10 years ago, the number has swelled to at least 30, including Own Beetles in North Point, Beetles Land in Mong Kok and Beetle Station in Sheung Wan.

Li has also benefited. Starting with one shop in Tsuen Wan two years ago, he now runs two other outlets, in Lam Tin and Tsim Sha Tsui, and a 1,500-sq ft farm in Tuen Mun, where he breeds nearly 200 species of beetles.

Prices have soared accordingly. A pair of giant burrowing cockroaches, a species native to Australia, can cost about HK$9,800.

Li says the internet has catalysed the trend for keeping exotic pets. His website has attracted 2,000 members who share experiences in raising the beetles and post photos of their prize specimens. 'The more customers understand about beetles, the more they are willing to spend on them,' he says.

At the Reptile Paradise shop in Mong Kok, Vincent Cheung Nai-chun also attributes growing interest in exotic pets to internet forums.

Cheung, who opened his second-floor shop on Tung Choi Street about 15 years ago, imports tortoises, snakes, lizards and frogs from around the world, mostly from Africa and South America.

Thanks to the surge, he may sell up to 20 snakes a month, including pythons, Honduran milk snakes and boa constrictors. Other popular reptiles are the African spurred tortoise, which costs about HK$650, leopard geckos, and colourful corn snakes that require little care and cost HK$400.

'Owners like to talk about their pets. And unlike dogs and cats, there is more to talk about with exotic pets, such as their origins, living environment and unique behaviour,' Cheung says. 'People, especially the younger generation, enjoy talking about their experiences on the internet forums and chat rooms. There are social elements that have accelerated the trend.'

But the popularity of exotic pets has raised concerns about the effect of the hobby on natural habitats and wildlife conservation.

'Animal lovers should ask where those exotic pets come from since not all species can be bred in captivity. Creating demand for endangered species makes one an accomplice to their extinction,' says Dr Alan Leung Sze-lun, senior conservation officer at the World Wide Fund for Nature.

In the past two years, the Agriculture, Fisheries and Conservation Department has recorded 14 cases involving 1,260 exotic reptiles being smuggled into Hong Kong as pets. (Trading in endangered species is an offence liable to a maximum penalty of a HK$5 million fine and two years in jail.) But dilemmas can arise even with exotic pets that aren't endangered. The imported animals can threaten fragile local ecosystems and humans too.

Licences are not required to keep snakes such as pythons or the Brazilian rainbow boa, which can grow to more than two metres in length and live for 20 years in captivity. Yet there may be a tragic price if owners fail to secure their cages, as happened in Florida in June when a toddler was strangled by an escaped python. In Britain, there have been several reports this year of pet pythons swallowing dogs and cats. The more common problem is with people buying exotic species without researching them and abandoning the animals when they find they're too difficult to maintain, or just get bored.

The discovery of alligator gar fish in the ponds of public parks in September is an example of this. Local shops sell the fish, native to North and Central America, when they are less than 30cm long. But owners eventually realise the gar are too big for home aquariums as they can grow to three metres in length and weigh 90kg, and many just dump them in a convenient body of water. Alien species often die after being abandoned because Hong Kong isn't their natural habitat, Leung says. Some even dump tortoises - a land-dwelling reptile - in the sea.

Yet survivors can also pose a threat to native flora and fauna. Exotic species can upset local ecosystems as they prey on native species or compete with them for food and habitat, he says.

For example, mosquito fish, which are native to North America, are widely blamed for decreasing numbers of Hong Kong's endangered Romer's tree frog because they feed on its tadpoles and spawn.

Anthony Yeung Ka-man, chairman of the Hong Kong Society of Herpetology Foundation, cites the red-eared terrapin or slider as a potential threat. Although native to the southern US, they've adapted well to local conditions. The female can breed from the age of two and lay up to three clutches of eggs a year, each containing as many as 20 eggs.

Because terrapins have the potential to multiply rapidly, 'there's high risk that it may replace native turtles', Yeung says. 'These days, pet shops offer all sorts of creatures that we never imagined existed. But you should really think twice before taking them home.'