From the road, their encampments look like igloos tucked among the trees. Up close, the squalor is clear. Piles of garbage and flies are everywhere. Old clothes, stiff from dirt and rain, hang from branches.

“There is everything in there,” said Diego Cañamero, the leader of the farm workers’ union in Andalusia, which tries to advocate for the men. “You have rats and snakes and mice and fleas.”

The men in the woods do not call home with the truth, though. They send pictures of themselves posing next to Mercedes cars parked on the street, the kind of pictures that Mr. Jallow says he fell for so many years ago. Now he shakes his head toward his neighbors, who will not talk to reporters.

“So many lies,” he said. “It is terrible what they are doing. But they are embarrassed.”

Even now, though, Mr. Jallow will not consider going back to Gambia. “I would prefer to die here,” he said. “I cannot go home empty-handed. If I went home, they would be saying, ‘What have you been doing with yourself, Amadou?’ They think in Europe there is money all over.”

The immigrants — virtually all of them are men — cluster by nationality and look for work on the farms. But Mr. Cañamero says they are offered only the least desirable work, like handling pesticides, and little of it at that. Most have no working papers.

Occasionally, the police bring bulldozers to tear down the shelters. But the men, who have usually used their family’s life savings to get here, are mostly left alone — the conditions they live under are an open secret in the nearby villages.

The mayor of Palos de La Frontera did not return phone calls about the camp. But Juan José Volante, the mayor of nearby Moguer, which has an even larger encampment, issued a statement saying the town did not have enough money to help the men. “The problem is too big for us,” he said. “Of course, we would like to do more.”