On Sunday, May 8, Sandy and I led a butterfly walk at Miller Woods and Miller Beach in Lake County as part of the Indiana Dunes Birding Festival. We met the outing participants at the Indiana Dunes Visitor Center, gave a brief PowerPoint show to introduce them to butterfly identification and a few of the special butterflies of the dunes, then carpooled to Miller Woods. Our target species for the morning was one of those special species, the Olympia Marble, which in Indiana can only be found at the dunes or sometimes at Kankakee Sands fifty miles to the south.
The Olympia Marble (Euchloe olympia) is a small, white butterfly, with greenish-yellow markings (and a rosy blush when freshly emerged) on the underside of the hindwings. With a wingspan of only 1 1/4 inches, it is at least 1/4 of inch smaller than its ubiquitous relative, the Cabbage White (Pieris rapae rapae). The Olympia Marble is one of our “spring ephemeral” butterflies—adults can only be found flying in early spring for a short period of time, perhaps two or three weeks. Eggs are laid on Sand Cress (Arabidopsis lyrata), its only known larval host in Indiana, a plant that is also restricted to the dunes and sandy soils of the northwestern corner of Indiana.
After mating, the female lays eggs singly on or near the developing flower buds. The larvae emerge from the egg in a few days and consume the buds, flowers, and seed pods. They reach maturity and become a chrysalis in about two weeks. The entire rest of the year, from early summer through fall and winter to the following spring, is spent as a chrysalis. The adult butterfly finally emerges in early spring, usually mid-April to early May at the dunes.
Our group of eight participants walked the old railroad bed through Miller Woods, spotting many American Ladies (Vanessa virginiensis), nectaring on dandelion. There seem to be more American Ladies on the wing this spring than in past years, it will be interesting to see if their numbers fluctuate during the year. We also saw a few Cabbage Whites, a brown blur that might have been a Mottled Duskywing (Erynnis martialis) (some friends from Ohio saw one later in the day), and a couple Clouded Sulphurs. Shortly before the bridge separating Miller Woods from Miller Beach, Christine Gerlach, Education Programs Ranger/Specialist for the Indiana Dunes National Lakeshore, spotted a small white butterfly flying among a patch of Sand Cress. It was an Olympia Marble! Sandy was able to net it (we had special permission to do so during this outing from the Superintendent of the Lakeshore) and coax it into a plastic container with paper towel (the paper towel provides the butterfly a place to perch and protects its wings). Everyone was able to get a close-up look at this gorgeous butterfly. We then released it and watched it continue on its mission. After crossing the bridge, we found two more Olympia Marbles nectaring on Sand Cress. Both were unusually cooperative and provided many good views and photo opportunities.
Although I did not take any photographs myself during the outing, shown above are some from my previous trips to Miller Beach and nearby West Beach, where Olympia Marbles can also be found.