millions of red crabs haven't managed to reach the sea. 数以百万的红蟹未能成功抵达海洋

247. There are 50 million of them.
     迁徙的红蟹数量多达五千万只
248. It's an event that has brought the island worldwide fame.
     这一景象让这座岛屿举世闻名
249. But in recent years,
     但近些年来
250. millions of red crabs haven't managed to reach the sea.
     数以百万的红蟹未能成功抵达海洋
251. An invader has occupied this island.
     一种入侵物种占领了这座岛屿
252. Yellow crazy ants.
     黄疯蚁
253. They escape from visiting ships, and with no predators
     它们搭乘来访的船只来到岛上 由于缺乏天敌控制

来自《行星地球 第二季 第一集 Planet Earth S02E01 岛屿》第 250 行