All of the forty largest global conurbations are migrant-rich whirlpools of human diversity. Taken together, those forty megacities have a bit less than 18 percent of the world's total population - but they generate two-thirds of the world's economic activity, and they're at the forefront of technology and science.

That's one of the striking findings cited in a new report presented on Monday in Berlin by Jochen Oltmer, a researcher at the University of Osnabrück's Institute for Research on Migration and Intercultural Studies (IMIS). The report, entitled "interrelationships between migration and development," was sponsored by two German non-government relief agencies, Welthungerhilfe and Terre des Hommes.

It's an indication of the powerful benefits migrant workers can bring to their new homelands. And the benefits flow in the other direction too: "Remittances of money from migrant workers back to their families in their countries of origin often go toward paying for education and health care, as well as consumer goods," said Oltmer.

"Workers returning to less-developed countries after a stint abroad can also bring new skills and capabilities back home with them, which benefits development," he added.

But migrant workers also face severe challenges - and so do their families back home. There are high social costs involved when someone spends years abroad, working under often very harsh conditions.

Migration downsides

Sita Ghimire, program director of the "Safer Migration Project" (SaMi) for the Swiss development agency Helveta in Nepal, said 29 percent of Nepal's GDP was funded by remittances from Nepali migrants working abroad - mostly in the Gulf Arab states or in Malaysia.

While that money can substantially improve the material conditions of the family members left behind in Nepal, "a family father might see his wife and kids for only a couple of weeks a year, for years on end," she said. "His children grow up without a dad at home."

For women, the social costs of migrant work can be very high as well. Ghimire said wives of Nepali migrant workers are often "blamed and shamed" if they have no husband at home, and thus subjected to hateful gossip and social exclusion.

Nepali women who work abroad - mostly as housekeepers in the homes of prosperous Gulf or Malaysian families - are extremely vulnerable to abuse.

"Housekeeping doesn't count as work under Gulf law," according to Ghimire. Women are trapped behind household walls with no one to turn to for support, "so there are no protections."

If a woman gets pregnant - in some cases because a male member of the household where she works has forced himself upon her - and she isn't legally married, then under Gulf law, she is put straight into prison, since extramarital sex is forbidden.

If she's legally married to someone back home, and can prove it, she won't be put into prison. But when she gets back home, her child may not be eligible for citizenship - and she's likely to face ostracism.

Complete work in DW