Did super-intelligent Martian bees visit Earth in flying saucers to observe us and examine the stockpile of gold at Fort Knox, concerned that we were on the verge of destroying the Sun? According to Gerald Heard in his book The Riddle of the Flying Saucers: is another World watching? (1950), that is the only conclusion that agrees with the facts surrounding the riddle of the saucers.
I have the original UK edition; there's also a US edition with the title and subtitle flipped. (The 1953 Bantam edition has two new chapters covering sightings outside the US and up to '53, among other changes -- full text here).
This was the second nonfiction book ever published on the flying saucer phenomenon, the same year as The Flying Saucers Are Real by Donald Keyhoe. Although Keyhoe's book was more influential among UFOlogists, Heard's cover art matches more closely what became the popular image of flying saucers, even if his theories about the saucers' pilots were more unconventional.