The most common and most likely answer to this crossword clue is the 9 letter word WOODLOUSE
I've seen this crossword clue in The Times
W
O
O
D
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O
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Buddy explains!
The straight part
We know that "Simple creature" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case simple creature = woodlouse.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does WOODLOUSE mean?
WOODLOUSE noun- Any of the terrestrial isopod crustaceans of suborder Oniscidea, which have a rigid, segmented exoskeleton, often being capable of rolling into a ball, and feed only on dead plant matter, usually living in damp, dark places, such as under stones or bark.