TOTTENHAM, Australia — The stench hits you first, pungent, musty and rotting. Then you hear them: a sound like ocean waves, or pouring rain hitting concrete. And the occasional squeak.

The horror lurking in the darkness is a throng of thousands of mice swarming above, around and inside a storage bunker of wheat at the Fragar family’s farm seven hours west of Sydney, Australia. After a long and painful drought, the mice are ravaging the family’s first good harvest in years and endangering the next one, putting their business on the brink of ruin.