TERESA VEGA’S first son was two when a flood carried rubbish, dead animals and disease through the canals of Oaxaca, her desperately poor home state in southern Mexico. The boy started vomiting, got diarrhea and ran a fever. There was a doctor a few hours’ walk away, but Ms Vega and her husband, Marco Lopez, had no money to pay him. They could do nothing, she says. They watched their son die.

Ms Vega now says this event is the reason for everything she and her husband have done since. When they had another son, Erminio, they decided that they had to make money in case he also fell ill. But Oaxaca offered them no jobs, save for a bit of maize-harvesting every July. Teresa’s younger brother Felix had already left for America to find work in California’s fruit and vegetable fields. In 2005, seeing no alternative, Ms Vega and her husband set out to follow.

Little Erminio would not have survived the journey, so Ms Vega and her husband had to leave him behind, in the care of Mr Lopez’s father. Erminio was one at the time. That was the last time Ms Vega saw him. Now 26, though she looks a decade older, she knew she was running another risk, because she was seven months pregnant again. But she and her husband made their way north nonetheless. Then came the crossings.

The crossings-invariably plural, because most attempts fail, leading to deportations and renewed attempts-are a seminal event in virtually all the stories of the undocumented farmworkers who labor in America’s fields. The border is their threshold and their first glimpse of El Norte, the promised land in the north.

But for la migra, as they call America’s immigration and border officials, it’s “like catching deer,” says Felix. He and his wife and cousins, six in total, were deported three times before succeeding at the fourth attempt, and the humiliations at the hand of la migra still sting.