Turtle said to metamorphose, sound as an insect (10)

I believe the answer is:

stridulate

I'm a little stuck... Click here to teach me more about this clue!

'metamorphose sound as an insect' is the definition.
I can't tell whether this definition defines the answer.

'turtle said' is the wordplay.
'turtle said' anagrams to 'STRIDULATE'.
Though, I am not sure how this is indicated.

'to' is the link.

Can you help me to learn more?

(Another definition for stridulate that I've seen is " Make scraping sound".)

I've seen this clue in The Times.

Want a hint initially instead of a full solution? Install my app