Every year during the summer solstice, a dog-eating festival takes place in Yulin, a city in the southern Chinese province of Guangxi.

This year’s event ended with the usual controversy. Photographs of dogs being fried or treated cruelly went viral.

Animal-rights activists and American congressmen demanded that China ban the eating of dogs and cats, as Taiwan did in April.

Yulin’s local government took modest steps to restrain or hide some of the more contentious activities, such as selling dogs in food markets.

Still, the festival was packed. Why has the controversial culinary habit become so popular in China?

Contrary to cliché, dog meat has not always been a common item in the Chinese diet. Unlike in the West, eating dogs has never been taboo, but it appears to have been rare in the past, reports the Economist.

Government accounts single out butchers who sold dog meat, suggesting it was unusual and worthy of record. According to Guo Peng of Shandong University, one of the few people to have studied the dog-meat market, only China’s ethnic Korean minority eat dog with regularity. The majority Han population, she argues, see it as a medicinal food, which is believed to warm the body in winter or cool it in summer—hence the timing of the Yulin festival at the mid-year solstice, literally the dog days of summer. Traditionally, Mrs Guo says, most people have only eaten dog once a year, if at all. According to a survey conducted in 2016 by Dataway Horizon, a polling firm, and Capital Animal Welfare Association, a Chinese NGO, almost 70% of Chinese people say they have never eaten dog. Of those who have, most claim they did so by accident—when invited to a social or business dinner, for example.

So why is the Yulin festival packed? And why do restaurants in many cities proudly put dog on the menu? The one-word answer is: criminality. Dog meat, a bit like drugs, has become a lucrative source of criminal income. For the past decade Mrs Guo has been going from village to village in Shandong province, on the east coast, asking inhabitants what has been happening to their animals. In one, villagers told her that a third of their dogs had been stolen between 2007 and 2011. Hunters, she discovered, have been roaming the countryside in vans, killing dogs with poisoned darts and selling them on to middlemen. Hunters got about 10 yuan ($1.30) for a kilogram of meat, so a medium-sized dog might be worth 70-80 yuan. One young man she interviewed was hunting so he could earn enough to get married. Hunted dog meat has increased the supply and lowered prices (compared with what they were), boosting the size of the overall market. Mrs Guo thinks Shandong and neighbouring Henan now supply a significant portion of China’s dog-meat business.

In a way, the dog-meat trade exploits the fact that modernisation in these provinces is incomplete. In villages, dogs are still guardians. In big cities, they are increasingly pets. The number of dogs registered as pets in Beijing (for example) has been growing at 25% a year for a decade. It now stands at about 2m, more than in New York. Concern for animal welfare has been growing in parallel, indicated by an increase in animal hospitals, animal-rescue and adoption agencies and changing attitudes. Increasingly, animal-welfare concerns are coming into conflict with dog hunters and dog-meat eaters. Eventually they will probably snuff out the trade.