Brer at PowerOfBabel has graced us with an excellent post on scarecrow lore, Season of the Scarecrow:
No-one really knows the origin of the scarecrow. Some hold they derive from the old Roman custom of having a herm in every field, and are thus of sacred origin as a guardian of the crop. According to one tale they arose from a grim necessity. In the old days it was the task of the very old and the very young to protect the fields from birds and other marauders by shrieking, waving their arms, or chasing them away when they approached; so the weakest and feeblest could still serve the needs of their folk. When the Black Death swept across the land, the old and the young were hardest hit. In their absence, and with spare clothes suddenly in abundance, the scarecrow was created to fill the gap, and since then its' enigmatic figure has strode across the landscape of our imagination.It is that time of year, after all. And there's a little bit of pipe-smoking lore in it as well.