Fly's last to escape insectivore (5)

I believe the answer is:

shrew

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'insectivore' is the definition.
(I know that shrew is a type of insectivore)

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for shrew that I've seen before include "Small mouselike animal" , "Woman to be tamed?" , "Small insectivore" , "Insectivorous mammal" , "difficult woman" .)

I've seen this clue in The Independent.

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