Meet Your Neighbors

Hairstreaks:
The Delicate Dozen

During the longest summer days at Gensburg-Markham Prairie in southern Cook County, shrubby prairie willows peek just above the grasses and flowering forbs. The landscape itself is picturesque, but if the observant naturalist looks closer, she may find something even more majestic flitting amongst the thistle and butterfly weed.

Acadian hairstreaks (Satyrium acadica) call this south-suburban prairie home every summer. These ghostly gray butterflies sport a row of submarginal orange spots and an orange cap over the blue spot on the hindwing. Their adolescent lives begin in April, when bright green caterpillars emerge from eggs that have survived the previous summer, fall, and winter on prairie willow twigs. The hungry youngsters then spend a month and a half munching on the nutritious willow leaves before they retire to a chrysalis and wait to emerge as adult butterflies. Unlike monarchs, these butterflies don’t have hanging chrysalises but pupate flat against surfaces.

When the adult Acadian hairstreaks emerge in late June and July, they have two or three exciting weeks of eating and breeding ahead of them. With wings spanning all of one inch, they collect nectar until they lay eggs in late July. Since Acadians spawn only one new generation each year, this is the only time they can be seen. Hairstreaks stay generally rooted to one place all year, restricting themselves to localized colonies even more than many other non-migratory butterflies.

This life cycle is typical of members of the hairstreak subfamily, 12 species of which can be found in the Chicago Wilderness region. Most of these species are only subtly different from one another in appearance, characterized by streaks of color — usually orange and blue — on the underside of their gray or brown wings, and short, hair-thin tails protruding from the wings’ trailing edges.

Yet, despite these similarities, the tastes and habitats of native hairstreaks can be as different as night and day. Doug Taron, curator of biology at the Peggy Notebaert Nature Museum (see the museum’s interactive Butterfly Lab online), explains that many hairstreaks spend their lives completely separated from other hairstreak species. “Each species has its own habitat,” he says, “but the group is going to be all over the place.”

For example, while the hickory hairstreak likes to spend its time around deciduous forest trees, coral hairstreaks like to feed on butterfly weed in prairies and shrublands.

And while the banded and the Edwards’ hairstreaks both frequent oak savannas, the banded hairstreak tolerates more degraded places, even semi-suburban landscapes, as long as oak trees are present. Butterfly monitors find the Edwards’ much less frequently. “They require a healthier savanna,” Taron says of the finicky Edwards’, “but exactly how they’re more picky or why they’re more picky, we don’t know.” You may find the Edwards’ in areas where a diverse plant community grows in the bright, patchy sunlight beneath widely spaced oaks.

Though the Edwards’ is a more conservative species, none of the Illinois hairstreaks are seriously threatened. While some native species seem rare in our area — the white m hairstreak, for instance — Taron explains that this is only because we are on the edges of their ranges. Partly because of data collected by volunteer butterfly monitors over the past two decades, he’s confident that no species have disappeared from our region.

Yet, to maintain this healthy multiplicity of native hairstreaks, Chicago Wilderness must continue to offer a wide variety of suitable habitats. Since this group of butterflies is a diversely particular group, the region must retain its wetlands, prairies, woodlands, and savannas for each species to continue to flourish.

— Tegan Jones

To become a volunteer butterfly monitor, call (847) 464-4426 or click here.