According to the U.S. Centers for Disease Control and Prevention (CDC), the plan failed almost immediately because mongooses are active during the day while the cane-field rats were mostly nocturnal, so the rodent population went largely unchecked.
Freed from natural predators and with abundant food, the mongooses reproduced rapidly and spread across the island, becoming an invasive species. Their diet expanded beyond rodents to include birds, reptiles, amphibians and other small native species, disrupting local ecosystems and causing severe harm to native fauna. The CDC notes similar outcomes occurred on other Caribbean islands where the species was introduced.
What began as an agricultural fix turned into a lasting environmental problem that continues to affect biodiversity today.