Crossword Genius

Host is shot when it gets a bit cooler (5)

Ross

I believe the answer is:

swarm

'host' is the definition.
(I've seen this before)

I cannot understand how the remainder of the clue works.

(Other definitions for swarm that I've seen before include "Group of social insects" , "Find insect population" , "Plague of insects" , "Climb; cluster of bees" , "Moving crowd, of bees say" .)

I've seen this clue in The Guardian.
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