It is difficult to see, but it works.
The screwworm, a particularly unpleasant kind of blowfly, used to attack cattle — and sometimes people — in the southern states. In 1959, a wall was put up and how the fly is gone, although it has recently reinfested the Florida Keys.
Since the fly mates just once in its lifetime, entomologists reasoned that if they could flood the zone with sterile males, none of the females’ eggs would hatch and the fly would be eliminated.
(This technique has been used with fruit flies in Hawaii, but with less success, for several reasons, one of which is that fruit flies mate more than once.)
So a gigantic screwworm fly hatchery was established in Texas. During peak seasons it was using 200,000 pounds of pork lungs a week to grow flies. The females were killed and the males were irradiated to sterility and released by the tens of billions along the border with Mexico.
I have my doubts whether the enviromaniacs would permit this today; they panic at the word radiation, but this was in the ‘50s.
Soon enough the flies were gone from the United States. By 1991 they were gone from Mexico, too, and today the technique is being used to push them back in Central and South America, although it seems unlikely they can ever be completely eliminated from the jungles. Presumably the flies re-entered the Keys from Central America.
What, you are asking, does this have to do with Trump and his fantasy wall to keep out Mexicans? Nothing, it’s just a curiosity, and a signal of the modernization of Mexico as it grows in wealth.
And perhaps that Robert Frost was wrong when he said good fences make good neighbors.