People passionate about nature

The Endangered Mottled Duskywing

The Mottled duskywing butterfly in Manitoba

by: Justis Henault and Richard Westwood

Justis Henault is a MSc student in the Bioscience, Technology and Public policy program at the University of Winnipeg, researching endangered Poweshiek skipperling larval feeding ecology and other Lepidoptera-at-risk. Dr. Richard Westwood is a faculty member researching at-risk butterflies and moths in prairie and forest habitats in the Departments of Biology and Environmental Sciences and Studies at the University of Winnipeg.

Mottled duskywing is a butterfly species, belonging to the skipper group of butterflies, living in pine parklands in eastern North America. It has been assessed as endangered in Canada by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). The population of Mottled duskywing found in Manitoba is called the Boreal unit.

Above: Figure 1. Adult Mottled duskywing (Erynnis martialis) nectar feeding on a Narrow-leaved New Jersey tea (Ceanothus herbaceus). © Justis Henault.

The Mottled duskywing is beautiful to watch in it’s habitat!

It is dark brown, has silvery scales that cover portions of the wings (sometimes mixed with iridescent purples), and also has distinct black marks on the wings. The hind pair of wings are brown with only black and yellow-brown marks (Figure 1). The brown underside of front wings have small white and black marks along the tips. It is about 3 cm long from its head to the tip of its abdomen, and its wingspan is approximately 5 cm wide.

Mottled duskywing is in the skipper group of butterflies, aptly named for their characteristic skipping technique while flying (Layberry et al. 1998). Of the two skipper groups, Mottled duskywing are in the Pyrginae subfamily. The other subfamily, called the Hesperiinae, contains the endangered Poweshiek skipperling butterfly.

Pyrginae subfamily butterflies rest with their wings open directly facing the sun, while Hesperiinae butterflies usually orient their hindwings to the sun and hold their forewings at 45 degrees. Many Pyrginae skippers in Manitoba are similar. They have black-patterned wings and white spots, they fly as early as June and into late summer, and may live in pine or mixed deciduous forests.

Species similar to the Mottled duskywing include the Sleepy duskywing (Erynnis brizo), Dreamy duskywing (Erynnis icelus), and Juvenal’s duskywing (Erynnis juvenalis) (Layberry et al. 1998). The Mottled duskywing can be accurately identified using present black markings and iridescent scales, and is larger than Dreamy duskywing while smaller than Juvenal’s duskywing.

Above: Figure 2. Location supporting Mottled duskywing in Manitoba. A sandy path dips down to a Ceanothus herbaceus plant adjacent to a Pinus banksiana forest. © Justis Henault.

Locations that support Mottled duskywing in Manitoba (Figure 2) can be found in Jack pine (Pinus banksiana) forests with sandy soil, such as Chokecherry (Prunus virginiana) and Saskatoon berry (Amelanchier alnifolia) shrubs, Hoary puccoon (Lithospermum canescens) and Big bluestem (Andropogon gerardi) (Plant scientific names in article sourced from Tropicos.org (2021)).

These pine forest habitats are beautiful and we encourage you to visit! Most Mottled duskywing habitat occurs on provincial crown land, permitted for recreation hiking and photography, berry picking, tree harvest, Indigenous plant and animal harvesting, dirt bikes and hunting (Agriculture and Resource Development 2021).

Above: Figure 3. Narrow-leaved New Jersey tea (Ceanothus herbaceus) plant in Jack pine forest ecosystem. © Justis Henault.

Mottled duskywing adults emerge between the last week of May and early June, flying until the first weeks of July in Manitoba. Adults nectar on New Jersey tea (Dodgson 2020), Dogbane (Apocynum spp.) and other species blooming during the butterfly’s flight period. During this time, they find mates to create fertile eggs for females to lay on nearby vegetation. New Jersey tea (Ceanothus spp.) shrubs are exclusively used as egg substrates (Committee on the Status of Endangered Wildlife in Canada 2012). Serrated green leaves on stems up to approximately 50 cm above the ground with white flowers distinguish these plants (Figure 3).

As seen in other butterfly species, female Mottled duskywing lay eggs in the sunny canopy of the host plant, which is likely to provide specific development temperatures required by eggs (Dempster 1997). Eggs have a ribbed shell – called the chorion – that displays interesting egg architecture (Figure 4).

Above: Figure 4. Mottled duskywing egg on Ceanothus herbaceus leaf bud. The chorion’s structure shimmers in the sunlight. © Justis Henault.

After egg development is complete, caterpillars (also called larvae) hatch out of their eggs, and eat New Jersey tea leaves. Shelters are made using leaves bound with silk at feeding locations (Figure 5). These shelters likely deter parasites, such as parasitic wasps, from consuming developing larvae as observed in other butterfly species (Morse 2017).

Above: Figure 5. Caterpillar in shelter made of Narrow-leaved New Jersey tea leaves bound with silk. © Justis Henault.

Caterpillars have brown-black heads adorned with red dots above the eyes, and pale green bodies. Caterpillars feed throughout the entire summer, developing through several instars – growth stages – until the fall. Larvae are thought to feed until winter, hibernate in dead leaves at the base of plants (Olson 2002), and either feed again in the spring or pupate until they emerge as an adult. We are currently preparing research manuscripts that attempt to answer these questions.

Prime habitat occurs in provincial forests and parks in south-central and eastern Manitoba. The provincial government of Manitoba manages these areas using silvicultural techniques (actively promoting forests with certain attributes), and provides business opportunities for the forestry industry (Agriculture and Resource Development 2021). These forests have been disturbed by wildfires throughout their development, and continue to experience periodic events to today.

Wildlife can continue to live in forests, cultural needs can be fulfilled, recreational opportunities can be enjoyed and economic activities can be realised by appropriately stewarding forests (Kimmins 2004). Disturbances such as wildfires and tree harvesting may stimulate forests to grow at an earlier development age, creating habitat for potentially different species than mature forests (Kimmins 2004).

In Manitoba where cottages or parks are popular, alternative strategies to create healthy natural spaces while reducing the risk to properties are used instead. Along with other researchers, we are researching specific forest management approaches that may improve the quality of Mottled duskywing habitat, as well as other insects, plants and wildlife that use these areas.

It appears that when these forests are disturbed with wildfire or silviculture methods at certain time intervals, the forests may provide an appropriate amount of sun exposure for Mottled duskywing and New Jersey tea host plants to flourish.

“What can I do to help?!”

We encourage you to continue learning about Mottled duskywing, and steward your natural spaces in ways that may stimulate healthy habitats! Share your passion about butterflies with others, encouraging people in your community to learn about local wildlife. Please help enthusiastic young people pursue an academic degree to research new approaches to humbly live with Mottled duskywing and natural habitats!

 

References
Agriculture and Resource Development. 2021. Forestry. Province of Manitoba. Available from https://gov.mb.ca/forest/forestry/index.html. [accessed 26 April 2021].
Committee on the Status of Endangered Wildlife in Canada. 2012. Committee on the Status of Endangered Wildlife in Canada assessment and status report on the Poweshiek skipperling Oarisma poweshiek in Canada. Committee on the Status of Endangered Wildlife in Canada, Ottawa, Canada.
Dempster, J.P. 1997. The role of larval food resources and adult movement in the population dynamics of the orange-tip butterfly (Anthocharis cardamines). Oecologia, 111: 549–556. https://doi.org/10.1007/s004420050270.
Dodgson, D. 2020. Recent Observations of the Mottled duskywing in Sandilands provincial forest, Manitoba. Blue Jay, 78: 26–27. https://doi.org/10.29173/bluejay6290.
Kimmins, J.P. 2004. Forest ecology: a foundation for sustainable forest management and environmental ethics in forestry. In 3rd ed. Prentice Hall, Upper Saddle River, New Jersey, United States of America.
Layberry, R., Hall, P. and Lafontaine, D. 1998. The butterflies of Canada.
Morse, D.H. 2017. Where should I lay my eggs? Oviposition choices of a shelter-building moth and the shifting danger of being parasitized. Entomologia Experimentalis et Applicata, 165: 1–8. https://doi.org/10.1111/eea.12625.
Olson, S. 2002. Conservation assessment for Mottled duskywing (Erynnis martialis). Eastern Region, USDA Forest Service. 9 pp.
Tropicos.org. 2021. Missouri Botanical Garden, Saint Louis, Missouri, United States of America. Available from: https://www.tropicos.org/ (April 28, 2021).