The most common and most likely answer to this crossword clue is the 9 letter word BOOKLOUSE
I've seen this crossword clue in The Times
B
O
O
K
L
O
U
S
E
Buddy explains!
The straight part
We know that "Tiny animal" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case tiny animal = booklouse.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 BOOKLOUSE mean?
BOOKLOUSE noun- Any of the small insects who feed on bookbindings, especially those of the order Psocoptera.