As cute as a bug's ear
Imagine for a moment a bug's ear... Cute picture? Hardly. You are more likely to be imagining something that might be at home in The Day of the Triffids. Do bugs (that's insects if you are reading in the UK) even have ears? Again, hardly. Many of them can detect sound, but they use a variety of strange means of doing it and none of them comes equipped with anything resembling a human ear.
Similes of the type 'as white as snow', 'as busy as a bee' almost always refer to a property that is archetypally appropriate for the item in question. So why would anyone have imagined a bug's ear to be especially cute?
The phrase originated in the southern states of America in the latter part of the 19th century and is still more common there than elsewhere. I've never heard it in conversation here in Yorkshire for instance. No-one, even in Texas, where the phrase is often said to have originated, thought that bugs' ears were cute. What they did think, and they had a point here as insects can detect very miniscule and high-pitched sounds, is that they were 'acute'.
'Cute' was a synonym for 'acute' in the 1700s in England. Nathan Bailey defined it in The Universal Etymological English Dictionary, 1731, as:
Cute: sharp, quick-witted, shrewd.
The term crossed the Atlantic and in 1848 the US romantic poet James Russell Lowell used the term with the 'sharp; shrewd' meaning in The Biglow Papers:
Aint it cute to see a Yankee Take sech everlastin' pains?
An early example of 'cute as a bug's ear' is found in a story in the South Carolina newspaper the Charleston Sunday News, June 1891:
Imogene McGinty is as cute as a bug's ear.
From around that time onwards, in the USA, the 'pretty; charming' meaning of cute began to supersede the previous 'acute' meaning, although the earlier meaning persisted for much longer in the UK, where it is still used.
Other 'as cute as' phrases came later and all of them rely on the present day 'pretty; adorable' meaning. Examples are 'as cute as a kitten/button/cupcake'. The expression 'as cute as a bug in a rug' is also quite commonplace. Bugs in rugs can't be said to be either especially sharp-witted or cuddly and that odd simile is just a merging of 'as cute as a bug's ear' and 'as snug as a bug in a rug'.
So, if you want 'cute', try a baby panda - bug's ears are 'acute'.
See other 'as x as y similes'.