The term "invasive species" sounds like an alert that aliens have arrived from a remote planet. Should we be preparing for a confrontation with extraterrestrials? The truth is there is plenty of danger to be found right here on Earth from our own "aliens". Invasive species are defined as non-native species whose introduction is likely to cause harm to the economy, environment or human health. Invasive species may introduce diseases, compete with native species for necessary resources, or directly kill the native species. This destruction can result in huge financial losses. It is estimated that the economic cost to the US of invasive species is between $100-200 billion per year, greater than all other natural disasters combined! It is easy to understand why John L. Schnase, the principal investigator for the joint NASA / U.S. Geological Survey invasive species project has called the threat of invasive species " perhaps our most urgent economic and conservation challenge."