Time to fight invaders If scriptwriters need ideas for a horror movie, they should check out the new statewide invasive-species management plan. Some of the descriptions of the non-native plants and animals threatening Arizona can make your skin crawl. Crayfish, for instance. They're no big deal in their home territory. But in Arizona, where they're not native and have no natural predators, they are creepier than the Creature from the Black Lagoon. When crayfish get into an Arizona pond or stream, they start off by gobbling all the insects. As their population grows, they tear into the frogs and fish. Then they strip out the plants. In the end, when there's nothing else left to eat, they turn cannibal, devouring each other. The management plan, adopted by the governor this month, does a vivid job of laying out the scary scenarios. Quagga mussels invading our reservoirs, where they can cause millions of dollars in damage by clogging pipes and watercraft. Buffelgrass taking over swaths of the Sonoran Desert, where it competes with signature plants like saguaros, paloverdes and even creosote bushes. The plan is a lot hazier on the solution side, however....