The most common and most likely answer to this crossword clue is the 8 letter word HOUSEFLY
I've seen this crossword clue in The Times
H
O
U
S
E
F
L
Y
Buddy explains!

The straight part
We know that "Insect" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case insect = housefly.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 HOUSEFLY mean?
HOUSEFLY noun- Any fly regularly found in human dwellings.