Organising colonisers, half of them initially (5,9)

I believe the answer is:

large intestine

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But I can't explain it at all! Could you help me understand?

(Other definitions for large intestine that I've seen before include "Part of one's innards" , "food processor" , "part of digestive system" , "this processes waste" .)

I've seen this clue in The Hindu.

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