WWU Environmental Studies grad student models potential habitat for highly endangered local butterfly

Their story unfolds like the opening scene of an action movie. Our hero, the island marble butterfly, faces unrelenting odds, dodges nemeses, and steels itself against a panoply of existential threats, from urban development to climate change.

The island marble (Euchloe ausonides insulanus) is a medium-sized butterfly with a wingspan of less than two inches. In flight, they can be confused with other white butterflies like cabbage butterflies. But when they are at rest, you can see that the underside of their creamy white wings is painted with their namesake yellow-green marbled pattern, and their bodies are fluffy. 

There are only a couple hundred island marbles left. The entire known population lives within one, approximately 800-acre prairie on San Juan Island. They spend almost 11 months of the year as chrysalises while we hold our collective breaths waiting to see how many will return in the spring.

Emily Bradford completed her master’s degree in Environmental Studies at Western last summer, where she used geography and GIS (Geographic Information Systems) techniques to model the very specific land cover and climate characteristics within the island marble butterfly’s niche habitat to determine where they might thrive into the future. Her thesis is titled “Finding Space for the Island Marble Butterfly.”

“It’s hard to think of any species that’s more of an underdog,” said Bradford. “The island marbles are a contender for the most endangered butterfly on the entire planet.”

A history mystery

When she settled on the island marble’s habitat as her thesis topic, Bradford read everything she could find about the butterfly.

Records of the island marble butterfly on Vancouver Island date back to 1861. But after a 1908 sighting on Gabriola Island, one of the Gulf Islands between Vancouver Island and mainland British Columbia, as far as anyone knew, they completely disappeared. Then, in 1998, seemingly out of nowhere, they were spotted on San Juan Island by Washington Department of Natural Resources zoologist John Fleckenstein.

Before smartphones and tools like iNaturalist were ubiquitously helping us identify insects, it’s possible they were just out of view of expertly trained eyes.

“They just vanished from the historical record for 90 years,” said Bradford. “There are so many unanswered questions about their history. We don’t know how they got here. We don’t even know how they got across the Cascades in the first place.”

The island marble is one of seven known subspecies of the large marble butterfly. The others are found on the east slope of the Cascade Mountains and across western North America. The island marble is unique in that it is the only one found west of the Cascades, and its yellow and green hues are more muted.

The island marble butterfly was classified as an endangered species under the federal Endangered Species Act in 2020.

Professor of Environmental Studies Aquila Flower, who teaches geography, is director of Western’s Spatial Institute and is also Bradford’s faculty advisor, explains that the reason it took so long to list them as endangered is simply that scientists thought they were already lost.

“There was no petition filed earlier because people thought they were completely extinct. Nobody even knew they were there to monitor them or talk about their endangerment,” said Flower. “If we’re not even aware of the species ever having been present, of course nobody’s worried about it.”

A few years ago, Flower was approached by the U.S. Fish and Wildlife Service seeking assistance with the spatial analysis component of a conservation plan for the island marble.

An uphill flight

The island marble butterfly faces many challenges. 

Their habitat needs are highly specialized. They like open spaces, so if they fly into a forested area, they will turn around and fly right back out. They will choose one of just three host plants — all in the mustard family — where the butterflies will spend most of their lives. 

Then there’s the island marble’s life cycle, which closely follows the life cycle of the host plant.

Adult butterflies emerge in the spring and, for about a week and a half, fly around, feed on nectar, find a mate, and lay lots of eggs in the flowers at the top of the host plant. Caterpillars hatch a week or so later. The young caterpillars can only eat very soft plant matter, so they eat the flowers and, as they grow larger, start to work their way down, eating the tougher parts of the plant. After a couple more weeks, they wander up to four meters from the host plant looking for an appropriate low-lying woody stem, where they attach themselves with a silk harness and form a chrysalis. Here they will spend up to 11 months encased as they transform from caterpillars to butterflies. Meanwhile, San Juan Island transitions from summer to fall to winter to a new spring. When the metamorphosis is complete, a butterfly emerges sometime between early April and late June, and the cycle begins again.

That’s almost an entire year camouflaged as a twig.

Island marbles are a single-brood butterfly, meaning they have only one generation per year, and their longest life stage occurs over winter. In the Pacific Northwest, it’s common for butterflies to overwinter as chrysalises, or pupae, because it’s their non-feeding stage. Multi-brooded butterflies like the cabbage white reproduce several times per year, so you see multiple generations each summer, making it seem like they are around longer.

A lot can happen during a long overwintering. Anything that threatens the plants — human interference, mowing, insecticides, deer and other mammals browsing — also threatens the butterflies. The island marbles are also subject to predation by spiders and wasps, mostly while in their larval stages.

Because the island marble’s life cycle is so aligned with the life cycle of their host plants, if there’s a mismatch due to any reason — like excess rainfall or drought — and the flowers bloom too early or late, the caterpillars could starve. With only one remaining population, this kind of event could be catastrophic for the species.

Professor of Biology Merrill Peterson, who curates WWU’s insect collection, worked with the U.S. Fish and Wildlife Service in 2008 to develop the initial monitoring plan for tracking the island marble population. Peterson implemented survey methods for understanding the size, makeup, and movement patterns of the population. 

When spring rolled around that year, Peterson and two other researchers were out surveying every day the weather was decent.

“The very first island marble we found that spring was on a cold day when it actually flurried a little bit in the morning,” said Peterson. “I wasn’t sure we were going to see anything, but we stuck around. There was a sun break, and one flew by. It was the first one anybody had seen that year. Most people were not looking yet because it was so cold.”

At the time, surveys found the distribution of island marbles was more widespread than it is today, including multiple locations on San Juan Island and one on nearby Lopez Island. The prior year, other researchers had found another population on San Juan Island, in a park at the site of a retired gravel pit on Pear Point south of Friday Harbor. 

“It looked like a great population because there were a lot of butterflies,” said Peterson. “But it was appearing to be what we call a ‘demographic sink,’ basically a kind of a dead-end spot to lay their eggs.”

The population there was almost entirely male. Male butterflies are generally smaller than the females, so they grow to their larval stage more quickly. Peterson hypothesized that because the gravel soils didn’t retain moisture well, once the temperatures heated up, the host plants died off before the slower-to-mature females could finish developing. 

With so little time in their adult stage, everything has to align just right.

A weedy disposition

When she was doing research for her thesis, it’s no wonder Bradford kept asking herself, ‘How on earth is this species still here?’ 

She said one positive of the island marble favoring just a few host plants is that it makes habitat restoration a bit easier. Just grow those plants. 

“Essentially, it’s just planting field mustard anywhere it will grow in this area,” said Bradford. 

One of the interesting aspects of this butterfly is that they are a native, endemic species whose preferred host plant is a non-native, introduced plant that has naturalized. Naturalization occurs when a non-native species persists in an ecosystem without significantly disrupting it. To most people, and especially farmers, mustard is a weed. Only one of the island marble’s potential host plants is native to the area — Menzies’ pepperweed — but the butterflies seem to prefer run-of-the-mill field mustard.

Flower says planting field mustard runs counter to the usual conservation and restoration thinking.

“It’s this weird story where conservationists are trying to protect a non-native plant. It’s a weedy thing that grows in fields, so planting it and then keeping it from being mowed or burned or grazed at the right time of year is key,” said Flower. 

“So, yes, let’s protect this non-native mustard species,” she said. “You’ve got to do extreme things when you’re facing such extreme endangerment.”

At home on the prairie

Island marbles are usually found in open prairies, occasionally along the borders of agricultural fields, and, historically, in coastal grasslands. 

American Camp, where the only known population of island marbles remains, is a former 1800s U.S. Army post that is now part of the San Juan Island National Historical Park. It is the largest remaining prairie in the San Juan Islands.

The only reason this prairie, in a tiny corner of San Juan Island, even exists today is because of its historical status. The National Park Service is obligated to maintain it in the condition it was in when its historical significance was established. 

“Something like 97% of the prairies we used to have in western Washington are lost at this point. Primarily to agriculture in the 1800s and the first half of the 1900s,” said Bradford. “Over the past 50 years or so, most of what we’ve lost has been encroachment by Douglas fir forests taking over because of the lack of fire and the lack of disturbance.”

Flower says the prairies and grasslands like those the island marble butterfly needs are often formed by fire.

“You only get grasslands when there is disturbance on the San Juan Islands,” said Flower. “You need the places disturbed enough to have this kind of open grassland environment, but then not let it be disturbed for long enough that the butterfly can’t persist.”

There have been reports of island marbles seen leaving the habitat at American Camp, but so far, none have successfully formed new communities. Either they leave and come right back, or they leave and do not survive. But the survival instincts are there; they want to create a new community. 

Peterson points out that this doesn’t mean they can’t or haven’t tried. 

“Clearly, at some point in the past, they have done some island hopping, even to get here from their native range before they became island marbles,” said Peterson. “Moving is just part of their natural dynamic. If a female that had already mated got caught by some winds flying across the water, it’d be pretty easy to end up getting deposited somewhere. The more people look, the more people start to realize rare, long-distance dispersal events do happen.”

Redundancy redundancy redundancy

For long-term survival, a species needs sufficient genetic variation to adapt to changing conditions.

“The one thing you don’t do as a species is have all your genetics in this tiny little one basket,” said Flower. “It’s terrible. So risky. And thus, this focus on let’s just get new habitat ready and hope we can somehow get population numbers up again, so we have a little redundancy.”

“Redundancy is the key,” she said. “Having multiple different habitat patches so one fire, one flood event, one predation event doesn’t take it all out.”

Place is an integral part of ecology, and is where Flower says Bradford’s research comes in.

“So much of ecological research is spatial,” said Flower. “It’s geographical data and spatial patterns. You can’t really protect a species if you don’t know where it can potentially persist.”

To find new potential habitats, Bradford began by scouring historical records to build a database of every known sighting of the island marble.

She used this spatial, temporal, and climate data to create a habitat suitability model that identifies possible locations for the butterfly in areas throughout the Salish Sea ecoregion, especially in the rain shadows of the Olympic Mountains and Vancouver Island. Bradford took into account historical and predicted climate conditions to identify places where host plants can grow and where land use, land cover, and soil drainage match the island marble’s habitat needs. 

Bradford’s model identified and ranked the most suitable sites. The most promising six she found are predominantly agricultural and residential land located on San Juan Island, Lopez Island, Orcas Island, two on Whidbey Island, and in Dungeness in Clallam County. 

She also created a sequential ranking of the sites to help prioritize where restoration and reintroduction efforts should happen first, based on those most likely to succeed.

“If island marbles succeed on San Juan Island and Lopez Island and we have a stable population there, we should look at Whidbey Island,” explains Bradford. “If they succeed there, we should look at Clallam County, but we probably shouldn’t try to go directly from San Juan Island to Clallam County because Whidbey Island looks like it’s better habitat.”

There are many direct and indirect effects that make the future uncertain, including the fact that we don’t know precisely what the climate will look like in 50-100 years.

“What’s suitable today might not be suitable a few decades in the future,” said Bradford. “For various reasons — it could be land use change or climate change — you can’t always guarantee an area you’re conserving right now is actually going to be a good area long term.” 

Fortunately for them, the island marbles prefer warm, dry summers, aside from habitat loss due to sea level rise, climate change appears to be less of a concern for them than for some other species. 

“It seems like American Camp is good for the island marble long term,” said Bradford. “And the other areas where I found suitable habitat also seem to be pretty stable over the next century or so.”

The butterfly effect

Flower says one conservation strategy is to connect habitat areas like stepping stones so that butterflies can travel between sites.

“Right now, they’re on islands, and then their habitat is like little islands on the islands,” said Flower. 

Currently, there is no way to create a pathway away from American Camp without crossing private land, which is one reason conservationists are looking for a lot of community support.

“This is going to require the involvement of private landowners in a way that might not be true for all endangered species. We just don’t have enough protected park land,” said Flower. “In an interesting way, protecting this butterfly gives us a reason to maintain some agricultural fields and not let them turn into forest, but create and maintain areas intentionally for the species.”

Bradford included agricultural land as possible habitat, even though those areas would need private landowners’ involvement.

“If we didn’t count privately owned agricultural fields, the amount of suitable habitat for the butterfly would decline by about 80 or 90%,” said Bradford. It varies from island to island, but some, like Lopez Island, have almost no native grasslands left.

One bright note is that because the island marbles are small, they don’t need huge patches of habitat. So, when asking private landowners to set aside space for them, it’s not a lot.

“There has been more and more community involvement in recent years, to the point that the island marble is almost — it’s not quite there — becoming like a mascot of the islands,” said Bradford. “People are getting really attached to this tiny little butterfly because it is, to my knowledge, the only endemic species that’s only found in the San Juan Islands. So, there’s this sense of local identity surrounding it.”

Bradford is working on a story map — a highly visual, interactive map of her research — where anyone can explore future homesites for the island marble butterfly.

With knowledge comes responsibility

Bradford speaks about the island marble with a sense of urgency.

“It’s nice to work on something so immediately important, with immediate practical applications,” said Bradford. “It makes me feel like, okay, maybe I’ve done something that is actually going to contribute to the survival of an entire species.”

Flower agrees that, while it can sometimes feel stressful, it’s also an incredible opportunity.

“There is such an urgency to this compared to a lot of research we do because, literally, in a year, a terrible thing could happen, and we could lose them,” said Flower. “And so, knowing where we can establish protected areas or land management practices that could help to save the species feels very important compared to any other research.”

“I’ve worked on so many different interesting research projects,” said Flower. “But none of them have had the dramatic plot arc of this one. Never such urgency.”

For now, we’re left with a cliffhanger while we anxiously await spring and the results of the next population count to see how our hero fares. If this really was an action movie, we’d all be lining up for the sequel.

Learn more about WWU’s Spatial Institute and degrees in Geography, GIS, and more in the  Environmental Studies department. The WWU Insect Collection, housed in the Biology Department, currently has about 80,000 specimens, is the largest public insect collection in Western Washington, and holds quarterly open houses.

Jennifer Nerad covers Western’s College of the Environment and College of Business and Economics for the Office of University Communications. Have a great story idea? Reach out to her at neradj@wwu.edu.