Coolbough Natural Area: oak savanna kept alive for a thumbnail-sized butterfly

There’s a butterfly here smaller than a postage stamp. It will only lay its eggs near one plant, and that fussiness is the reason a 400-acre patch of Newaygo County gets burned on purpose. The butterfly is the Karner blue, a federally endangered species. Its caterpillars eat exactly one thing — wild blue lupine — and that lupine grows at Coolbough Natural Area, a few miles outside Newaygo in Brooks Township.

Wild lupine grows in oak savanna. That’s the half-prairie, half-woodland ground where scattered oaks let enough sun through for grasses and flowers to thrive below. The habitat used to be common across western Michigan. Now it’s rare, because savanna only stays open if something keeps the brush from taking over. For thousands of years that something was fire. Snuff out the fires and the shrubs close in, the lupine gets shaded out, and the Karner blue has nowhere to lay eggs. So the people who care for Coolbough light slow, controlled burns to do what wildfire once did.

Brooks Township and the Michigan chapter of The Nature Conservancy put the preserve together, dedicating it in 2001 on land that had once been a struggling farm community. The foundations and field edges of those vanished homesteads are still out among the pines. Several loops thread through it — pushing past three small ponds and cattail marsh, up into white pine and white oak, and across the dry sandy openings where the lupine blooms purple in late spring.

Come in May or June and you might catch the bloom and, with luck, the butterfly itself: a flash of silvery blue, orange-spotted underneath, working the lupine in one of only a handful of western Lower Peninsula counties where it still hangs on.