Seems some native species are perhaps tiring of eating the same old native meal every day. According to this press release from the Georgia Institute of Technology, researchers offered two species of native crayfish (Procambarus spiculifer and P. acutus) a variety of native and non-native plants to eat - and they preferred the non-native plants 3 to 1! The results of the study are corroborated by other studies showing similar results for 9 herbivores taste-testing more than 300 plant species. This could throw a big wrench into the works that support the Enemy Release Hypothesis (the idea that invasive species are successful because they are introduced to new areas without the enemies that kept them in check in their native habitat).
If you're hard-core, you'll want to check out the full research paper by Parker and Hay, "Biotic resistance to plant invasions? Native herbivores prefer non-native plants" in the September issue of Ecology Letters - grab it here.