He said he met a young woman from Pingchang county, Sichuan province, who worked in Shanghai. Even though she had a 5-year-old child at home, she had divorced her husband and married a Shanghai resident. "She didn't care that the man had been divorced himself and that his legs were crippled," Shu said. "What she wanted was a foothold in the big city."

He also said migrant workers, especially those who work in catering and entertainment industries, will encounter various temptations at work. Many are seduced by the rich, who can offer them a higher standard of living.

Sociologists said the government should do more to help prevent families, the foundation of society, from crumbling.

"Local women's federations and governments in places that import labor should ensure migrant workers have a more colorful cultural life," Xia said. "They should give subsidies to left-behind spouses, to help them visit their partners."

Casual attitudes toward sex are also to blame, he said.

"People used to be faithful to their spouses," Xia Xueluan said. "But social and family values have changed."