Cost: $2 billion per year in the United States

Generally these tiny insects feed on plants, seeds and other small insects, but if given the chance may attack and even kill much larger animals. They swarm out of their mounds like a marching army and grip onto their prey with steely mandibles, injecting the prey with a dangerous toxin. For humans, it is quite painful, similar to a burn (hence the name). Most red ants tend to avoid humans and are generally kept under control by natural predators, but when they are introduced into environments that lack these predators, red ants can become serious pests.

Originally from South America, they were introduced to Mobile, Alabama via cargo ships in the 1930s. Since then they have gradually spread across much of the southwest. Today, many people still find these pesky bugs on lawns and in gardens, but only after the damage has been done. Sometimes they even find ways into the home, and can be a real threat to pets and even humans. Oddly enough, they seem to have an affinity for electrical wiring and air conditioning units.