Summer 1998

[TEXT ARCHIVE WEB-PUBLISHED MARCH 2002.
ORIGINAL PRINT PUBLICATION DATE: SUMMER 1998.]

Gems of the Bug World

By Jill Riddell

Contrary to what many conservationists have come to believe — that the greater the size of a natural area, the better its quality as habitat for plants and animals — researchers in the Chicago Wilderness region are discovering a more complex picture.

"The idea that 'big is better' is not as true as people think it is," says Ron Panzer. A conservation biologist with Northeastern Illinois University and manager of the Indian Boundary Prairies in Markham, Illinois, Panzer studies prairies and the organisms that live in them. A noted expert on insects, he has found that a tremendous number of butterflies and other invertebrates thrive on relatively small patches of prairie.

"At 1,500 acres, Goose Lake Prairie Nature Preserve in Grundy County, Illinois, has the same number of butterfly species as the Gensburg Markham Prairie has in 150 acres," Panzer says. "And I suspect the same is true for other insects."

This is encouraging news for local bugs and the people who love them. While the success of butterflies on small sites isn't an argument against increasing the size of nature reserves, in many cases natural areas are hemmed in by developed land impossible to acquire or restore. Until fairly recently, ecologists shook their heads over small sites and assumed they were seeing the last generations of prairie-dependent butterflies ever to grace those lands. The reasoning was that when a butterfly population is small, any unfavorable occurrence, such as a change in the water table or a blight on the caterpillar's host plant, might wipe out the population. While this possibility and the rule that large populations are less vulnerable haven't changed, Panzer and other insect specialists are finding that extremely rare species continue to surprise us all by thriving in precariously tiny spots.

Thriving on Small Sites

"For many insects, 20 acres may be large," Panzer says. "A 20-acre site can support numerous prairie-requiring butterflies."

As preserves go, even in the Chicago area, that's small. There's more land inside a highway cloverleaf. But there's evidence that butterflies requiring wetter-than-average conditions may be able to stick it out in patches even tinier than 20 acres. Doug Taron, a molecular biologist who has developed an expertise in Chicago region butterflies from a decade of intense study, knows of a privately owned, three-acre site in McHenry County in which Baltimore checkerspots, eyed browns, Acadian hairstreaks, and various sedge-eating skippers are getting along just fine. All are considered "remnant-dependent" species, meaning they can live only in high-quality natural areas.

While that's good news for butterflies that don't mind getting their feet wet, some upland species do seem to require stretches of habitat greater than 20 acres. Taron believes some species of butterflies of tallgrass prairie require closer to 100 acres of appropriate habitat.

And some species need much, much more than 100 acres. The regal fritillary in particular likes to stretch its wings and fly long distances. "The regal fritillary may require 1,000 acres," says Panzer.

While it is blessed with a rich array of butterfly life, the Chicago region also has the people resources necessary to understand butterflies well enough to help them thrive.

In northwest Indiana, Ralph Grundel of the U.S. Geological Survey's Biological Resources Division is running an extensive program to learn the habits of and improve conditions for the Karner blue butterfly. A federally-endangered species, the Karner blue's reliance on wild lupine as the sole food for its caterpillar is well-documented. But Grundel's five-year research program has gone far beyond such basics, helping biologists learn the insect's strengths and frailties.

It turns out that, unlike the free-ranging regal fritillary, a Karner blue stakes out a relatively small territory. In the Indiana Dunes, Grundel found it was unusual for a Karner blue to strike out farther than 100 meters from home, and less than five percent ever flew farther than 500 meters. Grundel's discovery teaches land managers that if habitat for one of the subpopulations in a chunk of lupine-rich oak savanna is ruined, the Karner blues can't just pick up and fly along to the next amenable remnant a mile down the road, the way some butterflies would. In fact, at the Indiana Dunes, the parkland is divided into east-west units separated by two steel mills. Karner blues number in the thousands on the west unit. None have been seen on the east since 1976.

Grundel also determined specific habitat needs of males and females. The males spend 90 percent of their time in sunny openings, while females spend time in sun and partial shade. The females can't know under what conditions lupines will fare best in a given year, so they lay their eggs in varying types of canopy. Research like this can help land managers make better decisions about how open a savanna should become, and how much shade is optimal.

Butterflies and Fire

Ron Panzer is in the process of completing a five-year study on the impacts of fire on invertebrates. He has found that in the year following a burn there are significantly fewer numbers of butterflies. However, one year later, the butterfly population has generally recovered. To survive long term, prairies require fire, and certain butterflies require prairie. So while individual eggs or larvae may be hurt by a fire, the population of prairie butterflies increases as the overall quality of the prairie improves.

One of the more inspirational efforts underway to protect Chicago's butterflies is the volunteer monitoring network led by Doug Taron, now of the Chicago Academy of Sciences. A crew of 45 lepidoptera-literate volunteers have committed themselves to monitoring butterflies at 35 sites around the region. The protocols are based on a British system in which an ecologist walks a predetermined transect across a preserve and records every butterfly identified within 10 meters of the path. Participants in Taron's network commit to visit their assigned preserves four to six times between mid-June and the end of July.

Over time, the information accumulated by the volunteer monitors becomes increasingly valuable. "Individual year-to-year variation doesn't mean very much," Taron says. Weather affects the growth of plants the caterpillars depend on, and one year there may be more parasites on that type of plant than in another, resulting in a temporary plummet. "We have to collect data long enough that real trends can be seen over the background noise."

With monitoring information in hand, managers can take butterflies' needs into account in decisions about habitat restoration. A simplistic scenario would be that the population of a particular butterfly living in a brushy prairie receiving no restoration assistance begins to decline. The land manager takes note of the butterfly monitor's report of diminishing butterflies, and therefore changes priorities for this site in restoration plans. Others can use monitoring data to educate county boards or state legislators about what land needs to be acquired to protect butterflies.

Butterflies as Barometers

Butterflies lend themselves well to a monitoring effort. The number of species is manageable; there are approximately 100 different kinds in the Chicago area. Unlike other insect groups, most butterfly species are simple to identify. One can study butterflies without having to destroy them, whereas some other insects are too difficult to conclusively identify in the field. Butterflies are active during the day, so researchers don't need special nighttime equipment. It's possible to survey butterflies without having a large impact on the preserve — many volunteers become proficient enough to identify them on the wing and don't need to catch them.

There are many readily available field guides. And about a third of butterfly species are dependent on high-quality natural areas. Both these factors make them a logical selection for study.

However, there are drawbacks to using butterflies as indicators of the health of an ecosystem overall. "They're just one group of insects," Taron cautions. "We couldn't possibly study each and every insect group as thoroughly. [Butterflies] are a good proxy, but you simply can't automatically apply what we know about butterflies to every other insect."

Still, before the butterfly network, most preserves had no monitoring of any invertebrate animals. Butterflies — and the folks who appreciate them — have added a new dimension to the stewardship of nature.

Jill Riddell is a writer who does most of her butterfly observing in parts of the Chicago Wilderness with a little less concrete than her Bucktown neighborhood. She writes frequently on nature for WBEZ Radio and Chicago Magazine.