Mottled Duskywing Butterfly
(Erynnis martialis)
Status: Endangered in Canada. Found only in Manitoba and Ontario. Extirpated in Quebec.
Species Identification:
The Mottled Duskywing Butterfly is a medium sized species with a wing span of 25 to 42 mm. Their wings are light brown with dark grey and yellow-brown spots which give it a mottled appearance. Interestingly freshly emerged adults actually have a purplish iridescence.
Mottled duskywing caterpillars have a bright lime green body with a dark orange/brown/black head and no long hairs.
Diet: What do they eat?
Mottled Duskywings have very refined tastes which consist of predominantly New Jersey Tea, Prairie Redroot and other species that are closely related to the two. Adults consume nectar from these plants and use them as host plants for egg laying. After eggs hatch, the caterpillars will remain on the plant and consume its leaves.
Adult males are also known to drink water and minerals from moist soils which he then passes to females during the mating process (nuptial gifts are common in insect communities) to improve the fitness of her eggs.
Habitat and Range:
Mottled Duskywings live in early to intermediate successional, partially shaded forests where their host plants, New Jersey Tea and Prairie Redroot, are found. (As a side note, other butterflies and even birds love these plants! Thus, consider adding them to your garden to attract more wildlife).
Unfortunately, Mottled Duskywings are only found in a few places in Ontario (these tend to be Oak Savannas) with 9 metapopulations believed to remain in Southern, Ontario. Within The Land Between the last publicly confirmed sighting was in Mamora in 2014. NOTE: it is probable that a few sights have happened since then, but due to their endangered status and poaching threats, these locations are known only to researchers.
Threats: Why are they a Species At Risk?
Habitat fragmentation: Mottled Duskywings have limited dispersal abilities due to their specific habitat and host plant requirements. Human development and land conversion have fragmented their habitat, making their populations isolated. This isolation makes it very difficult or nearly impossible for butterflies to travel between populations which results in a reduction of genetic diversity resulting in increased disease susceptibility.
Habitat destruction: Many of the remaining populations of Mottled Duskywing in southern Ontario occur in highly populated areas where there is an increased threat of habitat destruction due to human development (their savanna habitat makes for an extra easy development process compared to heavily forested areas for example). The Mottled Duskywing population in The Land Between is located on privately-owned land and has undergone development to become a subdivision, thus rendering the habitat no longer suitable for this species.
Succession and canopy closure: The range of the Mottled Duskywing is directly linked to that of its host plants, which require an open canopy. As human development has increased, forest fire suppression has allowed many canopies to close, rendering such habitats as no longer suitable for their host plants, and thus for the Mottled Duskywing itself.
Extensive herbivory: Heavy browsing by White-tailed Deer damages or removes host plant leaves, resulting in a reduction of the available food and egg laying locations for the Mottled Duskywing. Such herbivory also results in direct mortality of eggs and larvae.
Invasive species: Foreign species like Dog Strangling Vine (DSV) have expanded into the Mottled Duskywings range and are now threatening the species. DSV in a vigorous grower that, when introduced, can dominate habitats by growing in thick clusters. These groupings can be so thick that they block light from reaching the ground and shade out any other species that do germinate. Thus, the expansion of DSV into the range of New Jersey Tea and Prairie Redroot (Mottled Duskywing's host species) has resulted in their suppressed growth, which has reduced Mottled Duskywing butterflies' populations. Climate change could aggravate this by making it easier for various invasive species to overwinter.
Pesticides: Spraying of the pesticide Bacillus thuringiensis to control LDD moths (gypsy moths) is also proposed to have negative effects on Mottled Duskywing populations. Read our blog to learn more about BT and LDD moths.
Current Conservation Efforts:
A Mottled Duskywing Butterfly Recovery Strategy has been created for Ontario with the Ontario Butterfly Species at Risk Recovery Team playing a leadership role. Alderville First Nation, Pinery Provincial Park and the Nature Conservancy of Canada have also made, and continue to make, significant contributions in progressing the conservation of this butterfly. The aforementioned recovery strategy includes: habitat conservation, controlled burns, invasive species removal, and forest succession controls (not allowing habitat transitions to closed canopy forests in areas where the butterfly is found). Captive rearing and reintroduction projects are also underway and have shown some success. Click here to read an article by CBC on the success of Mottled Duskywing recovery projects!
Works Cited
- https://www.ontario.ca/page/mottled-duskywing-recovery-strategy
- https://www.ontario.ca/page/mottled-duskywing
- https://www.natureconservancy.ca/en/what-we-do/resource-centre/featured-species/insects-and-spiders/mottled-duskywing.html
- https://wildlifepreservation.ca/mottled_duskywing_recovery/
- https://www.onbutterflysar.com/current-projects/