The Visitors (novel)

The Visitors are simple black oblong boxes, as large as buildings, which approach from space and orbit the Earth before descending to the United States.

Eventually, they start producing vehicles, superficially resembling human cars but capable of flying using the same unknown principles as the Visitors themselves, and apparently incorporating some element of intelligence, or at least instinct, since they do not crash into things as they move.

Neither side ever makes any meaningful communication with the other, and the only real outcome of the contact is considerable frustration and the potential of large-scale damage to Earth's economic systems.

The idea of aliens' disrupting human economies also features in the author's earlier novels Ring Around the Sun (1953), They Walked Like Men (1962), and All Flesh Is Grass (1965).

Rosemary Herbert in her review for the Library Journal wrote that Simak has "produced one of the most engaging novels of alien invasion ever written".