My mother hated not only snakes but caterpillars too.

Literal

Mother [topic-は] snakes [topic-は] needless-to-say, caterpillars [even-も] disliked-[polite-past-でした]

~はいうまでもなく = 'needless to say about X' / 'not to mention X.' The pattern sets a baseline (snakes) and then extends to something that might be more surprising (caterpillars). も = 'also/even.'