Tom Peterson

12/27/2000

A total of 40 species of butterflies were seen on the Fermilab site in the year 2000, bringing the total for the past two years to 44 species. The variety of habitats--marsh, prairie, old field, and woods--with some of the wetlands and woods being old remnants make Fermilab an outstanding place for finding a good variety of northern Illinois butterflies. Although some rather uncommon butterflies and some remnant-dependent species have been observed on the Fermilab site, no federally or state-endangered species have been seen. The remnant-dependent species are mostly wetland species; no strictly prairie-dependent species have yet been observed in our prairie restorations.

The Purplish Coppers were abundant on site this year, again associated with Polygonum coccineum. Two areas hosting numerous Purplish Coppers were the mowed field around Bullrush Pond and the shore of Main Ring Lake near C4. Neither location is a pristine natural area; in fact the coppers near C4 were abundant on the weedy gravel berm separating Main Ring Lake from the Main Ring cooling ponds. I saw one Purplish Copper in May, several in July, and many in late August/early September. We clearly have a good-sized population of Purplish Coppers breeding on site. Wild Indigo Duskywings were also abundant this year and generally associated with Crown Vetch, which is abundant on site.

Of the ten new species seen this year, three (Delaware Skipper, Coral Hairstreak, and Northern Pearly Eye) are considered somewhat remnant dependent and are probably breeding on site. The Delaware Skippers and Coral Hairstreaks as well as a second population of Eyed Browns were found on the eastern edge of the site, south of Wilson Street in ELM-20. ELM-20, consisting of old fields with some wetland remnants under the power lines and along the railroad tracks, is interesting butterfly habitat which I hope to visit more in 2001.

Another area which seems to host a particularly nice variety of butterflies is the western edge of the Big Woods near the Prairie Interpretive Trail, in ELM-24. This area includes woodland species such as Commas and Pearly Eyes. The Banded Hairstreaks are found here, and the prairie/woods edge hosts numerous Great Spangled Fritillaries. Just a few yards into the prairie were Common Wood Nymphs. Every year I see a few Giant Swallowtails in the Big Woods area, the caterpillars of which may be feeding on Prickly-Ash in the woods.

Although in the 1999 Butterfly Report, I suggested adding some monitoring routes at Fermilab to the database maintained by the Northern Illinois Butterfly Monitoring Network, I have not yet done so. I still think it would be a good idea to establish some regular monitoring of populations on site. It would be particularly interesting to do so in our prairies in order to watch the development of populations of prairie species. However, I decided during the summer of 2000 that it was more interesting to continue to survey the site, to see what we have, rather than walk certain particular routes on a regular basis. The populations of remnant-associated butterflies such as the Banded Hairstreaks, Coral Hairstreaks, Purplish Coppers, Black Dash Skippers, and Eyed Browns are scattered in very local pockets over the 6000 acre site. Certainly more such local populations remain to be discovered, some of which could have implications for site management. Surveying the site will remain a high priority over the next few years.

The following table lists what was new for the year 2000 with some comments about each species.
 

New for 2000	Comments
Atalopedes campestris (Sachem)	A common southern species that disperses north by the end of the summer. I saw only a few individuals late in the summer.
Atrytone delaware (Delaware skipper)	A prairie/old field species that is probably breeding on site. These were seen in the center of the Main Ring and in ELM-20.
Epargyreus clarus (Silver Spotted Skipper)	A common and widespread skipper; surprising that I did not see it last year
Pyrgus communis (Checkered Skipper)	More common to the south. I only saw one, on the eastern side of the site.
Harkenclenus titus (Coral Hairstreak)	This looks like a local colony breeding on site in ELM-20.
Cynthia virginiensis (American Painted Lady)	Common, wanders widely, populations fluctuate
Polygonia comma (Comma)	Abundant this year in the woods and woods edge. No doubt breeding on site.
Libytheana bachmanii (Snout Butterfly)	Southern, wanders to the north, just saw this one individual.
Enodia anthedon (Northern Pearly Eye)	Common this year in the woods and woods edge. No doubt breeding on site.
Megisto cymela (Little Wood-Satyr)	Probably breeding on site in the woods; I only saw one but expect to find more next year.

The following four species of butterflies were seen in 1999 but not in 2000. The only butterfly which I really expected to find again and did not was the Acadian Hairstreak.
 

Seen in 1999 but not in 2000	Comments
Battus philenor (Pipevine Swallowtail)	This was an unusual stray which I would not expect to see at Fermilab
Eurema lisa (Little Yellow)	Wanders up from the south; not surprising to not find it every year
Nathalis iole (Dwarf Yellow)	Wanders up from the south; not surprising to not find it every year
Satyrium acadica (Acadian Hairstreak)	Probably breeding on site and missed it this year. This is one to look for in 2001.

Some information above about the habits of the species, as well as species identifications, were taken from the following references.

1.  "National Audubon Society Field Guide to North American Butterflies," by Robert Michael Pyle, Alfred A. Knopf, Inc., New York, 1981.
2.  "Butterflies through Binoculars, the East," by Jeffrey Glassberg, Oxford University Press, New York, 1999.