In the 1930s, South American fire ants likely arrived in Mobile, Alabama, in ship ballast soil, and today their stinging mounds cover much of the US South and cost billions to control

When cargo ships unloaded in the bustling port of Mobile, Alabama, in the late 1930s, little attention was paid to the soil used as ballast. After all, it was merely one of the many components of international business, an efficient method of ensuring stability when travelling across the Atlantic.

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