There’s a migration going on, though the skies aren’t yet dark with ducks or geese. Polk County naturalist Heidi Anderson explains this is the annual butterfly migration.She says in early September you see lots of monarch butterflies, especially where there are asters, goldenrod and thistle flowers. The black-and-orange-winged bugs are on the way from Canada to Mexico, and Anderson says volunteers can take part in a program to tag them for identification.Anyone who finds a tagged butterfly can send the tag number information to the address that’s on the small wing tag. She says Iowa’s been at the center of a controversy over whether the immature form of the monarch is harmed by corn engineered with a “B-T” gene to kill off pests.The caterpillars eat pollen while they’re feeding on nearby leaves of the milkweed. Some studies indicate the corn pollen kills them, while other studies refute that finding. Millions of the monarchs migrate each year across Iowa, though they die before it’s done and their eggs hatch to continue the trip. To learn more, surf to