Autumn Olive is an infamous invasive shrub well known for taking over fields from farmers and conservationists. But did you know the berries taste just like Sweet Tarts? No kidding. You don't eat them like normal berries, you suck on them and then spit out the big seed. This Autumn Olive was at the Ansonia Nature Center, but they are found throughout the area along roadsides and old fields. When ripe, the berries are red with little speckles on them, and one shrub can produce a huge amount of berries.
Unlike some other invasives, Autumn Olive does have value for wildlife. The berries are eaten by birds in preparation for fall migration, and the shrubs provide dense cover for nesting as well as erosion control. On the other hand, they quickly replace valuble hayfields and meadow habitats, and the fast-growing shrubs are a major hassle and expense to remove.
I have developed a grudging respect for some invasives. These plants and animals are marvelously competetive. They are simply better at what they do, which is why they win and take over.
Update 9/9/2008: A fascinating article in the NYTimes yesterday discusses how, in the big picture, contrary to conventional wisdom, exotic species actually contribute significantly to biodiversity and evolution. Which isn't to say that certain species don't cause terrible problems, just that the arrival of exotic species is not the end of the world.