Summer 2001

Baltimore Checkerspot
Gossamer Tapestry

When I was asked to write a profile of one of the region's butterflies, I wanted to choose a species that was strongly associated with natural ecological communities rather than parks or gardens. At the same time, I didn’t want to pick something that is so rare that it’s very difficult to get out and actually see the thing. Fortunately, it didn’t take much thought to come up with the ideal candidate.

The Baltimore checkerspot (Euphydryas phaeton) is a denizen of specialized alkaline wetlands called fens. Although fens are rare ecosystems, there are enough of them scattered throughout the area that it is still possible to find this butterfly on nearly two dozen sites in Chicago Wilderness.

The Baltimore checkerspot is named for Lord Baltimore, the colonial administrator of Maryland. Lord Baltimore’s heraldic colors are orange and black and have been remembered in naming such diverse orange and black creatures as the Baltimore checkerspot and Baltimore oriole. In a freshly emerged adult, the dominant black color of the upper side of the wings has a particularly rich, velvety texture. The scarlet and yellow spotting of the wings are vividly set off by this midnight black.

The colors that we find so beautiful in Baltimore checkerspots are unappealing to many of their predators. These butterflies have been shown to be unpalatable to birds, and the distinctive spotting pattern serves as a warning coloration, not unlike the more familiar monarch butterfly.

Adults are on the wing from mid-June to early August, with peak flight right around the 4th of July. Although strongly tied to their very specific habitats, they can be abundant when conditions are to their liking. At times, dozens can be seen taking nectar at flowers and basking in the sunshine. Males of the species are territorial and engage in vigorous aerial dogfights.

Female Baltimore checkerspots show an extremely narrow range of plants on which to lay eggs. In the Chicago region, turtlehead (Chleone glabra) is the only plant on which the females oviposit. Eggs are deposited in masses of several hundred on the underside turtlehead leaves. Newly laid eggs are vivid magenta. Within about a day, however, they fade to a rather unexciting tan. About three weeks later, the eggs hatch.

Newly hatched larvae migrate to the tops of the turtlehead plants where they spin webs and feed gregariously. In late summer, the larvae stop feeding and add substantially to the web. This thickened web can sometimes be seen a foot or two off of the ground around turtlehead stalks in late August and early September. Long thought to be where the larvae hibernate, this is actually a pre-hibernation web where the larvae spend late summer and early autumn. In late October, the larvae move out of the web and into the leaf litter at the base of the plants where they overwinter.

In late April or early May, hibernation ends, and the caterpillars resume feeding. Although they still feed on turtlehead, these post-diapausal larvae also feed on a much wider variety of plants. Some of these, like swamp betony, penstemon, and downy yellow painted cup are in the same family as turtlehead. However, the caterpillars eat many other species including ash, honeysuckle, plantain, and valerian. This wider range of host plants allows the Baltimore checkerspot to inhabit sites that contain insufficient turtlehead to function as the sole food source for an entire colony. The largest caterpillars can consume thousands of times more leaf material per day than newly hatched caterpillars. It is this most voracious stage that consumes the widest variety of plant species.

By early June, the larvae again cease feeding, and wander away from their host plant to pupate. The inch long chrysalis is a beautiful creamy white with orange and black markings. Metamorphosis is complete by mid-to-late June, when the first adults again grace the fens of Chicago Wilderness.

— Doug Taron