Population boom! An update on mottled duskywing numbers

Posted onAugust 17, 2023byElliot Santoni|Mottled Duskywing Butterfly, Native Pollinator Initiative, News and Events

WPC is working to bring the mottled duskywing back to Ontario as part of the Ontario Butterfly Species at Risk Team. Together, we are spearheading an innovative effort to reintroduce the duskywing to Pinery Provincial Park in southwestern Ontario.

The mottled duskywing reintroduction project at Pinery Provincial Park is well into its third year of bringing back the butterflies. Right now, we’re at the start of the butterflies’ second generation of the year. In Canada, these butterflies typically have one flight period — one generation of adults — per year. But here at Pinery, we’re far enough south that the butterflies have time for two flight periods! This gives the team more time to release butterflies, track population numbers, and monitor the habitat the butterflies use. In the time between flight periods, we’ve crunched some numbers, and come up with an amazing result.

Last year was the first year of monitoring populations after the initial releases in 2021. The results were promising, multiple years of releases are required to build a genetically diverse, self-sustaining population. At our most successful release site, Site A, we found less than 100 mottled duskywing in the wild last year, with around 30 in the first flight period.

A mottled duskywing, resting on my hand. Credit: Elliot Santoni

A mottled duskywing caterpillar, hiding in a leaf nest. Credit: Elliot Santoni

This year, at that same site, we’ve already found nearly 200 mottled duskywing, just in the first flight alone! That’s an increase of about six times, and we’re only halfway through the season.

The best part is, this increase has happened without any additional releases. This is because we separate our release efforts into three different field sites. Last year, we decided to focus all of our releases into the two field sites that were struggling to maintain a population, and didn’t release any butterflies into Site A.

Unlike monarchs, mottled duskywing don’t migrate to escape the cold. Instead, they spend the winter as caterpillars, hiding out in the fallen leaves beneath the snow to survive. This means that when the second generation lays their eggs, those larvae have to survive the winter. In the spring, they pupate and become adults, which then form the first flight period of that year. Despite hunkering down and entering diapause (a state of suspended animation, similar to hibernation), winter cold is not easy to survive for small insects. Many larvae simply do not survive until spring. Because of this natural winter die-off, the first flight period is often smaller than the second, which needs to be large to produce enough offspring to make sure some survive until spring.

What does this mean for us? Hopefully, it means an even bigger population boom! Since Pinery is the only place in Canada where mottled duskywing have two flight periods, there really is no predicting the size of the second generation. However, all signs point to exciting numbers in the final months of this year’s field season.

Elliot Santoni

Elliot is a graduate of Sault College, where he gained a dual diploma in Fish & Wildlife Conservation and Natural Environment Tech. He has a keen interest in insects, birds, and reptiles, and is always seeking opportunities to participate in conservation efforts.