A friend asked why something whimsical is also described as "maggoty." We can chalk up the explanation either to the capriciousness of our English language or to the fact that the meaning of a word can be transformed over time. Whichever theory you prefer, we wouldn't advise using the two terms interchangeably, although we do admit that maggot is—sometimes—synonymous with whim. (来源：英语杂志 http://www.EnglishCN.com)

Since the early 1300s, the word maggot has been used to name the soft-bodied legless grub that is the larva of a dipterous insect. Sometime in the early 1600s, the conceit of that baby wormlike feeding form that metamorphoses into another form took flight and developed a figurative sense naming a fantastic or eccentric idea, or whim. Ironically (or not), that fanciful meaning stuck around, and the changeable maggot also came to name a fixed idea or obsession.

On the other hand, the meaning of whim hasn't wandered all that far from its initial sense. Whim entered English in the late 1600s, a shortening of whim-wham, a whimsical object or device especially of ornament or dress. A whim is a fancy or a capricious or eccentric and often sudden idea or turn of the mind.