The mottled duskywing butterfly was on the verge of disappearing from Ontario. Now, a pioneering reintroduction effort is raising hope that this and other at-risk butterflies can be brought back to life

The drive from the Cambridge Butterfly Conservancy to Pinery Provincial Park on Lake Huron is a two-hour trip that Adrienne Brewster makes frequently. But when she set out for the park on the morning of July 21 last year, it was anything but routine—thanks to the precious cargo on her back seat.

Brewster, the conservancy’s executive director and curator and a key member of the Ontario Butterfly Species at Risk Recovery Team, was carrying coolers packed with live mottled duskywing butterflies—a handful of small, marble-flecked, brown adults and hundreds of tiny apple-green pupae, all hand-reared at the conservancy’s lab. It was a life-restoring mission for an endangered species whose Canadian populations are hanging on in a few isolated sites in southern Ontario and Manitoba.

Lost and found: The mottled duskywing recovery project is seeking to reestablish a mottled duskywing population in Pinery Provincial Park

Pinery, a 2,500-hectare sliver of protected land south of Grand Bend, contains one of North America’s largest remaining segments of oak savanna, a globally imperilled landscape that blends tallgrass prairie and oak forest, and for sustainability requires periodic burning. The park is also prime habitat for the mottled duskywing. But habitat neglect, overgrazing by deer and fire suppression may have contributed to the species’ disappearance; the last time anyone saw the butterfly there was in the early 1990s. Now, with the impending release of Brewster’s cargo—the first reintroduction of any endangered butterfly species every attempted in Ontario—that was about to change.

“It was a really, really special day,” says Brewster. “Lots of oohing and aahing and some tears.”

Jessica Linton, a biologist with Natural Resource Solutions Inc. in Waterloo who chairs the recovery team, was on hand—along with other partners from the team, park staff and even a documentary film crew—to meet Brewster. Both women had been working toward this moment for years, and it was “super emotional,” says Linton. Each member of the core team then carefully held and released one of the adult butterflies, watching them fly off into the oak savanna like missing puzzle pieces returning to the frame.

Over the following two weeks, with less fanfare, the group released more adults, pupae and larvae in two sections of the park, nearly 700 individuals in all. That was enough, the team hoped, to guarantee that by fall their would be plenty of larvae—the life stage in which mottled duskywings overwinter—to ensure that some would survive the cold and snow to emerge as adult butterflies next spring.

The team had reasons to be confident. Thirty years of oak savanna restoration at Pinery had created an abundant stock of New Jersey tea, one of just two plants on which mottled duskywings lay their eggs. Also, the five-year recovery plan is state of the art. It integrates population studies, genetic research and a ground-breaking captive-rearing program. “Their approach is leading the way,” says Jaret Daniels, a world-leading authority on butterfly conservation at the Florida Museum of Natural History with whom Brewster previously studied. “They’re viewing this from a very scientific angle and collecting a lot of data, which is going to feed into a much better understanding of what’s working and what’s not.”

For the balance of the season, the team continued monitoring in the park. The real test, however, would come the following spring, says Linton. “We’ll be waiting to see butterflies.”

Habitat restoration in progress: Prescribed burns have helped restore Pinery’s oak savanna ecosystem




Compared to charismatic endangered species, like the monarch butterfly with its brilliant colouring and epic migration, the mottled duskywing is a wallflower and a homebody. Dark, drab, not much bigger than a toonie, it flies low to the ground, quickly and erratically, making it hard to recognize. Never very abundant, historically ranging over the eastern United States and southern Quebec, Ontario and Manitoba, it lives in small colonies and, for the most part, never strays far from its locale.

The mottled duskywing’s decline in Canada mirrors its fate in much of its range, which has shrunk significantly in the past half century. Because the species depends on just two plants in relatively rare ecosystems, it is highly susceptible to habitat loss. Insecticides and herbicides are also a threat. Where it remains in Ontario, adult mottled duskywings fly from mid-May to early July. Farther south, a second brood will pupate and emerge as adults in mid-July to late August.

Despite the butterfly’s small size, the recovery project has a big backstory. In 2007, shortly after Linton completed a master’s degree studying butterflies, she won a contract to write a federal status assessment on the mottled duskywing population. Doing fieldwork in three provinces, “I spent a lot of time looking and not finding it,” she says

Largely on the basis of Linton’s research, the butterfly was deemed extirpated in Quebec and listed as endangered federally in 2012. Three years later, it was also listed as endangered in Ontario. Linton then produced a recovery strategy for the Ontario government, collaborating on more surveys to understand where the existing populations were and the threats to them.

In 2017, Brewster entered the picture. She had been working at the butterfly conservatory since the early 2000s while studying ways to help threatened butterfly species. By the time she and Linton crossed paths, Brewster was deeply involved with a recovery group eager to reintroduce another Ontario oak savanna butterfly, the Karner blue—a species last seen in the province in 1991.

Linton had also written a report on the feasibility of a Karner blue recovery. She concluded the chances were slim, in part because of the species’ unique need for a connected network of habitats. When she met with the Karner blue group (known as Karner Blue Ontario), “I walked away thinking, If I could just get these people to focus on the mottled duskywing… I think we could really have a case,” she says. The idea of a broader Ontario butterfly recovery team was born; the mottled duskywing was its first project.

The path from the formation of the team to the release last summer involved a dizzying array of fieldwork and lab research. The captive rearing, never before attempted with this species, was particularly complicated. First, what were hoped-to-be mated female butterflies were collected in the field and brought into lab enclosures with their host plants. Technicians fed them a nectar solution by hand and waited for them to lay eggs on the plants. Once the eggs hatched, each larva was transferred into its own small enclosure, fed by hand and nurtured to whatever life stage was required.

Room service: In the Cambridge Butterfly Conservancy lab, each mottled duskywing larva is hand-reared in its own chamber

While labour intensive, the process was far superior to simply collecting adult butterflies in one location and shipping them to another. “In captivity,” Brewster explains, “we can protect the more vulnerable life stages—the egg, the caterpillar and the pupa—from predators, disease and virus.” By doing so, the team increased the approximately 5 percent survival rate in the wild to 80 to 90 percent in the lab. It could also raise hundreds or potentially thousands of butterflies using only a few dozen captured females.

Brewster’s team at the butterfly conservatory first tried the process on a non-endangered “surrogate species,” the wild indigo duskywing. “We weren’t sure whether or not they would even lay eggs in captivity,” she says. “As it turned out, we had success right away.”

In 2019, the team repeated the process with a small number of mottled duskywings, using females collected from a population east of Peterborough. The researchers were permitted to capture the endangered butterflies only if they returned 20 new individuals to the original location for every female they had taken out. This meant that most of the offspring produced that year, and again in 2020, went back to the source, as planned.

The year 2019 was also pivotal because of a five-year, $825,000 grant the team received from the Natural Sciences and Engineering Research Council Alliance to fully implement the project. Besides the recovery team’s work, the grant covered multi-year studies of mottled duskywing populations in the Rice Lake Plains area led by Ryan Norris, a member of the team and a biology professor at the University of Guelph. Norris spearheaded the grant application. (There are other partners for the grant, the Nature Conservancy of Canada being the main one.)

The grant also covered critical genetic analysis, started in 2019, which was used initially to determine if the chosen source population held enough diversity to create a viable population at the release site. Nusha Keyghobadi, a molecular ecologist at Western University who directs that effort, says, “Nothing was really known about the genetic diversity of mottled duskywing.”

Snug as a bug: While mottled duskywing larvae overwintered on the ground in small nests inside curled leaves, the recovery team waited for spring to see if any would survive and fly as adults

On May 15, Linton was at Pinery with Norris preparing for this year’s field monitoring season when she got a text message that set her heart racing. A Pinery visitor had posted a photo on the iNaturalist citizen science portal of an adult mottled duskywing butterfly. “As soon as we saw that, Ryan and I headed out to the field, and we were able to see an individual [mottled duskywing] ourselves,” she says.

Almost immediately, Linton, Brewster and other team members were sharing “high-five” emojis. “I was just on cloud nine,” says Linton.

As of June 21, 32 mottled duskywing butterflies had been recorded at the two release locations in the park. Sightings of females laying eggs demonstrate they are successfully mating. The results brought heightened optimism as the team moved forward with its fourth summer of captive rearing, and the second summer of new introductions to bolster what is now a new resident population of mottled duskywing butterflies in Pinery.

Future plans include releasing captive-reared individuals in at least one other site as early as 2024. They have tentatively identified a location in Norfolk County where duskywings were once found, as well as an adjacent restored property the Nature Conservancy of Canada owns.

Linton has not forgotten the promise she made to Brewster and others with Karner Blue Ontario: that knowledge gained from the reintroduction of the mottled dusky- wing would lay the groundwork for future recovery programs for other endangered or extirpated butterfly species. “That’s how the recovery team was born,” says Linton. Now, having proved they could do it for one species, “we have a much better case to say, ‘Okay, let’s try it with others.’”

Marked for recovery: Team members monitor mottled duskywing numbers by capturing and marking them before re-release

This article was originally published in the Fall 2022 issue of Ontario Nature’s ON Nature magazine. Photos courtesy of: Pinery Provincial Park (first, second, fourth images); Ontario Butterfly Species at Risk Recovery Team.