There are lots of comparisons with animals in English, but the truth is that many of them
are seldom used nowadays. Maybe the animal kingdom has formally complained.
Here are some of these comparisons:
as bald as a coot
as close as an oyster
as dead as a dodo
as free as a bird
as mad as a March hare (as mad as a hatter is used instead)
as meek as a lamb
as happy as a lark
as pissed as a newt
as quiet as a mouse
as timid as a rabbit
However, some comparisons with animals are still relatively frequent:
as blind as a bat
as busy as a bee
as poor as a church mouse
as stubborn/obstinate as a mule
as proud as a peacock
Could you translate the idioms into Spanish and add to the lists?
To learn more comparisons with as, with their translations into Spanish you can consult my Diccionario Bilingüe de Modismos, pp. 30-35, Verticebooks, 2012.
Going by the book
Hace 2 meses