Tom Peterson
10/26/1999
Introduction.
A total of 34 species of butterflies were observed on the Fermilab site during this past summer. Four of these species (Black Dash Skipper, Eyed Brown, Bronze Copper, and Purplish Copper) are considered to be "remnant-dependent" and another seven species are remnant-associated. A judgement regarding which northern Illinois species are "remnant-dependent" or "somewhat remnant-dependent" may be found in "Butterfly Monitoring Guidelines for the Chicago Region"1 and in the northern Illinois "Butterfly Monitoring Network’s Guide to the Butterflies of Illinois".2 Quoting from the latter source, "The remnant reliancy refers to how reliant a species is on high quality natural areas to survive. If it is highly remnant reliant, it will only be found in the proper natural habitat. If it is somewhat remnant reliant, it may be able to tolerate some disturbance and loss of quality to its habitats."
All of the remnant-dependent and most of the remnant-associated butterflies seen this year at Fermilab were wetland species. Perhaps there were enough wetland remnants at the time of the founding of Fermilab to "re-seed" with butterflies the new wetlands that have formed on site. This appears not to have happened for prairie species. Although the prairie restorations now total many hundreds of acres, no really prairie-dependent butterfly species were seen.
Many butterfly adults only live a week or two, and the flight period for the local population may be only a few weeks. The intersection of the time of the adult butterfly’s life, the observer’s free time, and good weather can be rather small, so I had to limit my observations to what looked like some of the most interesting areas. I "spot-checked" various places on site, and also, at the start of the summer, I selected two "routes" to walk weekly which focussed on the prairie restorations: through the oldest restored prairie (Feldott Rd. and Holter Rd. through the center of the Main Ring, ELM-1) and through a new prairie and some mature woods (the Interpretive Trail and part of Big Woods, ELM-24 and ELM-25). Although these routes offer a nice variety of butterflies, neither route includes the sedge meadow hosting Black Dash Skippers and Eyed Browns, and neither includes the pond edges where I found Bronze Coppers and Purplish Coppers.
Notes.
A summary list of the 34 butterfly species seen this summer at Fermilab with links to photos of a few of the butterflies may be found in the Fermilab Butterfly Table. The following are comments about some of the species listed.
Banded Hairstreaks are found at the edge of an old, mature oak woods (ELM-24) in a route that includes the "Interpretive Trail" through a newer prairie restoration (in ELM-25). The woods edge and savanna also included numerous Great Spangled Fritillaries. It is a good place for spotting Giant Swallowtails; I have also seen them there in previous years. The Pipevine Swallowtails in ELM-25 last June were probably some kind of anomaly. The nearest population is probably in Waterfall Glen Forest Preserve, near Argonne Lab. (Strangely, that same day in June, I saw a Pipevine Swallowtail in my back yard in St. Charles. Perhaps someone released a bunch of them.) A couple of small, wandering Pieridae, Eurema lisa (Little Yellow) and Nathalis iole (Dwarf Yellow) are known to gradually disperse to the north through the summer, but then die back during winter since they cannot survive the winter this far north. Although they are not permanent residents here and tell us little about the site, they are rather unusual and were nice to find. Some other butterfly migrants, Precis coena (Buckeye) and Hylephila phyleus (Fiery Skipper), were unusually common this year and may have benefited from a relatively mild winter. Erynnis baptisiae (Wild Indigo Duskywing) was formerly rather uncommon, feeding as a larva on wild indigos, but now seems to have adapted to crown vetch as a larval host plant.3 That might explain its presence here.
A sedge meadow inside the Main Ring circle (in ELM-1 near ELM-3) is home to Black Dash Skippers and Eyed Browns. Larvae of both species feed exclusively on sedges. The sedge meadow is an area away from roads which I only visited once, but it would be worth monitoring next year. There are other patches of sedge meadow inside the Main Ring, which I also intend to explore next summer.
Perhaps the most exciting finds for me were the Coppers, both Bronze and Purplish. I had seen Bronze Coppers at the intersection of Feldott Rd. and Main Ring Rd. in June, and also observed them near A2 on the Main Ring last year. I had not seen Purplish Coppers here before. They seemed to be a bit more restricted to certain pond edges, and they are not quite as conspicuous in flight. It was only after chancing upon one Purplish Copper near some sandbar willows where I was looking for Cecropia and Polyphemus moth caterpillars in mid-August that I started searching similar pond-edge areas for Purplish Coppers. (Fermilab’s sandbar willows are host to giant silk moth caterpillars as well as many butterfly caterpillars, including Viceroys, Mourning Cloaks, and Acadian Hairstreaks.) By the end of the season I had found around a dozen Purplish Coppers over about a two-mile area through the center of the lab site. From late August through mid-September, Bronze and Purplish Coppers were flying along the Main Ring road and cooling ponds through B- and C-sectors, along ditches behind the Industrial Center Building parking lot, and around Bullrush Pond.
Although the Bronze Coppers at Nelson Lake Marsh live in the prime area of the marsh, at Fermilab so far I have observed both the Bronze and Purplish Coppers only in relatively disturbed areas. The Purplish Coppers were usually flying in patches of Polygonum coccineum. It is likely that Polygonum coccineum is serving as a larval host plant for the Purplish Coppers.
In the Fermilab Butterfly Table, the last column shows the number of northern Illinois butterfly monitoring network sites reporting each species. The fact that the Purplish Copper is only found at two out of the 29 sites monitored combined with its being considered highly remnant-dependent make it an exciting find. The Bronze Copper and Purplish Copper are two of the 27 butterfly species "that have declined over at least part of their range in the past 25 years,"3 due to habitat destruction.
Recommendations.
1. I suggest adding Fermilab to the sites monitored by the northern Illinois monitoring network, organized by Doug Taron and Ron Panzer. A beginner and/or non-Fermilab-employee could monitor the route through the Prairie Interpretive Trail and neighboring woods. This includes a nice variety of habitats, including mature woods, prairie restoration, and a savanna/old field region at the woods edge where the Banded Hairstreaks and numerous Great Spangled Fritillaries were found.
2. I will establish a route next summer through the interior of the Main Ring circle, which includes some of the best sedge meadows and oldest restored prairie. The presence of Black Dash Skippers and Eyed Browns gives me hope that other sedge meadow or marsh species may be found on site.
3. If it turns out that the Coppers are not found in the more undisturbed wetlands, a third route could follow a maintenance road along some cooling ponds where one could count Bronze and Purplish Coppers.
4. There are other areas on site which I did not visit but intend to explore next year. The intersection of free time, good weather, and right season can be rather small. It is hard to be in very many right places at the right time. Other nice butterfly species could be resident here; this season of observations was just a start.
References.
1. "Butterfly Monitoring Guidelines for the Chicago Region," by Ron Panzer, Don Stillwaugh, and Doug Taron (March, 1992).
2. "Butterfly Monitoring Network’s Guide to the Butterflies of Illinois," compiled by Doug Taron, edited by Mel Manner.
3. "Butterflies through Binoculars, the East," by Jeffrey Glassberg, Oxford University Press, New York, 1999.