People are noticing that spring is coming earlier, flowers bloom sooner, and summer has been lasting longer than in previous years, sometimes by a difference of one or more weeks. Bird migrations north and south have also changed, with bird watchers seeing species increasingly in northern climates where they have not before ventured. In North America, mammals such as opossums and armadillos are also increasing their northern ranges, and—a bit more worrisome—insects such as fire ants and Africanized bees are also moving north.