battlekruiser, i think Fargison thought u are referring to the zerglings as larvaes so he thought in order to obtain a location for all the larvaes he needs a location centered on the larvaes each distinguished by each player.
Well, thats what he thought ... but thats not how u do it.
I'll just build and elaborate on what DT_bc has said, well dattlekruiser is referring to the zergling as the 'bounders'. Each player controls them to dodge the larvaes. You centre a unique individual location on the zerglins each and when the players bring the zergling to a larva (with a location centered on the zergling), it will satisfy the trigger.
Condition-
'Obstacles' bring at least 1 larvae to 'Loation centered of zergling for X player'.
(its the same as u bringing the zergling to the larvae because the larvae has reached the location centered on the zergling)
Action-
Kill all 'Zergling' for 'Player X' at 'Loation centered of zergling for X player'.
Preserve Trigger.
Hope that helps, just re-enforcing what DT said, you should thank him

PS: i didn't proof read my post, this may not make sense.