Another creature many countries eagerly introduced to their homelands is the cane toad, a native of Venezuela and Guyana [source: Butler]. Like the European starlings, cane toads chow down on a lot of insects that can ruin sugarcane and other valuable crops. But these gigantic amphibians -- which can grow up to 15 inches (38.1 centimeters) long -- will eat almost any terrestrial animal, and fight with native amphibians for food and breeding grounds. Even worse, cane toads excrete a strong toxin from their skin that can sicken or kill domestic animals and wildlife, and even humans. People have died from eating the toads and their eggs, too [source: ISSG, WebEcoist].
Cane toads are especially problematic in the U.S. and Australia. In the latter country, some feel eradication is impossible because the toads' numbers are so great. One Queensland researcher is working on developing a strain of cane toad that can only give birth to males, ensuring the creatures' eventual demise, once the genetically engineered toads mate with regular ones [source: IMB - Institute for Molecular Bioscience]. However, only time will tell whether the cane toad or man is more resourceful -- and if we've finally learned our lesson about introducing non-native species into our homelands.