At a time of high unemployment, many Americans are convinced that these aliens take American jobs. As a test, this summer the United Farm Workers (UFW), the main agricultural union, launched a campaign called “Take Our Jobs”, inviting willing Americans to work in the fields. In the following three months 3m people visited takeourjobs.org, but 40% of the responses were hate mail, says Maria Machuca, UFW’s spokesman. This included e-mails such as one reading: “We’re becoming more aggressive in our methods. Soon it may come to hands on, taping bitches to light posts.”

Only 8,600 people expressed an interest in working in the fields, says Ms Machuca. But they made demands that seem bizarre to farmworkers, such as high pay, health and pension benefits, relocation allowances and other things associated with normal American jobs. In late September only seven American applicants in the “Take our jobs” campaign were actually picking crops.

That was the point, says Arturo Rodriguez, the UFW’s president. America’s farm jobs, which are excluded from almost all federal and state labour regulations, are not normal jobs. Americans refuse to do them. The argument about stolen jobs is “just a façade” for a coarser scapegoating, says Mr Rodriguez, and “we demonstrate the hypocrisy.