Cost: $300 million per year in the United States

Although they are not well known and rarely seen, the tiny Boll Weevil has, historically been one of the most harmful animals in the world. These tiny beetles grow to only about 6 millimeters but do incredible damage to cotton and flowers.

They’re originally from South America but crossed into Texas and eventually spread across the United States. In the 1920s they nearly destroyed the entire cotton industry in the U.S. and contributed mightily to the hardships of the Great Depression. Today, it is estimated that they do $300 million worth of damage every year.