Sure, maybe they've been observing Earth, but then, they'd probably know why the scarecrow was built, wouldn't they?

Actually, teleportation accident, alien invasion.

Secret of the Scarecrow World (1958). Writer: Gardner Fox. Art: Carmine Infantino. Based on a cover by: Gil Kane. A new teleportation device accidentally leaves a giant scarecrow off Earth's North Pole. This story shows many Fox techniques and themes. It deals with the invention of teleportation, and its use in space travel, a theme of Fox's Adam Strange tales and other works: Adam Strange was making his debut at the same time this story appeared. It features a married couple who work together as scientists, as in Fox's Space Museum stories, and elsewhere.

The story features a Fox cycle - for a discussion of Fox cycles, please see the article on Adam Strange. Here, teleportation from one location to another, then back again to the original location, is a complete cycle. As usual in Fox cycles, this leaves the original situation unchanged at the end. This cycle is close to the zeta-beam cycle in the Adam Strange stories, which also centers on teleportation between planets. In both cycles, there are strange features that affect the teleported half way through the cycle: charging with radiation in the zeta-beam cycle, change of size here. These cycles are also used in similar structural ways. Here Earth faces a menace (an interplanetary invasion), just as the planet Rann typically faces a menace in the Adam Strange tales. And the hero here uses the existing cycle to "interfere" with this menace, just as Adam Strange often uses his zeta-beam cycle to interfere with and defeat menaces to Rann.
Another structural use of the cycle recalling other Fox tales: the story includes a "change of protagonist for the cycle, on a massive scale", as in the Adam Strange tale "Planets of Peril" (Mystery in Space #90, March 1964).
This story also deals with another Fox concept: the cycle with a flaw in it. The time travel in "The Two-Way Time Traveler" (Strange Adventures #143, August 1962) is also flawed. Fox's dialogue actually uses the word "bug" to describe this engineering problem: an early use of this computer term in a fiction story.
While the story is based on a cover by Gil Kane, it twists the cover situation around, giving it a different meaning than it has in Kane's cover. It is more a rationalization of the cover, a plot dreamed up to "explain" it, than a straightforward use of the covers idea as a story premise. This is typical of the way Fox did not always closely use Kanes cover concepts.