The problem was that the times of the large-scale migrations were hard to predict, and a whole group would pass by a location in a short hour or two, so to be successful it was necessary to mobilize a lot of workers and station them at various locations.
問題是，蝴蝶大規模遷移的時間點難以捉摸，整群通過一個據點為時僅一、二小時，因此需要動員相當多人力，並在各地「佈樁」才可能達成。