The most common and most likely answer to this crossword clue is the 4 plus 5 letter word KIWI FRUIT
K
I
W
I
F
R
U
I
T
More clues leading to the result KIWI FRUIT
Buddy explains!
The straight part
We know that "Hairy grub" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case hairy grub = kiwi fruit.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.