Spring Dune Butterflies

Springtime is progressing nicely here in the Chicago area. Most of the trees are now in leaf. The daffodils are pretty much finished, and the butterflies are beginning to put in an appearance. Two species of butterflies here in northern Illinois put in a single, very brief appearance at this time of year. Both can be seen at Illinois Beach State Park, a dune habitat on Lake Michigan in the extreme northeast corner of the state.

The Olympia marblewing (Euchloe olympia) loves sandy habitats like the one found here. It’s a small white butterfly, with a beautiful greenish yellow marbling on the undersides of the hindwings. At Illinois Beach, you can see dozens of them, but only for a few short weeks in Late April and early May. The caterpillars feed on plants in the cress family. On this site sand cress (Arabis lyrata) is used. This butterfly is unusual because the adults also depend almost exclusively on sand cress as a nectar source. At this time of year, it’s just about the only nectar-producing plant blooming on this site. The butterfly in this picture is using it.



The hoary elfin (Incisalia polios) is much smaller than the marblewing, and pretty easy to overlook. The caterpillars of this species feed on bearberry (Arctostaphylus uva-ursi), a low mat-forming plant that grows on thee sand dunes. Hoary elfins are listed as an endangered species here in Illinois. In this case, I’m not really sure how necessary this status is. This butterfly was never a common species in the state. Illinois beach is just about the only place in the state where the host plant grows, and is home to the state’s only population of this butterfly. It’s very well protected as a state park. I’ve never gotten a good picture of this species myself, however one of the other volunteers at Bluff Spring Fen recently got a great shot of one at Illinois beach. You can see it here.

I love going out to the state park in the spring to visit these butterflies, however it can be a frustrating experience. The park sits right on the lake, which is still quite cold at this time of year. I have had several experiences of leaving my house on a beautiful day with temperatures in the mid seventies. After driving two hours to the park, I encounter a 20 mph wind directly off of the lake and temperatures in the mid forties. Still the butterflies are sufficiently uncommon, beautiful, and interesting to make multiple trips worthwhile. On a good day, you can see dozens of each species flying low over the sandy plains.