Mottled Duskywing

Erynnis martialis
Species Status: Endangered in Canada (COSEWIC assessment); Endangered in Ontario
Action Required: Population augmentation, reintroduction and/or assisted colonization

Mottled Duskywing (Erynnis martialis)

The plants that mottled duskywing larvae feed on require dry sandy areas or limestone alvars found in very few places in eastern Canada. Unfortunately, these sensitive areas are also prime sites for human development.

Characteristics

The mottled duskywing (Erynnis martialis) is a small to medium skipper butterfly, measuring 23 to 33 mm across the wings. It earned its common name from its wings which display a strongly mottled pattern of light and dark brown with yellowish-brown spots. It can be spotted in dry, open habitats like barrens, sandy patches in woodlands, oak savannas, tallgrass prairies, and alvars (limestone areas with sparse vegetation).

The male and female look almost identical. What sets them apart is the males possess a fold along the leading edge of the forewing that contains yellow scent scales used during mating. Females lack this specialized fold but overall have heavier mottling patterns than males, making them appear more distinctly patterned.

Similar looking species

  • Horace’s duskywing (Erynnis horatius)
  • Juvenal’s duskywing (Erynnis juvenalis)
  • Zarucco duskywing (Erynnis zarucco)

Habitat

Unlike many other butterflies that prefer lush meadows, mottled duskywings typically inhabit dry, partially shaded areas. These include sandy patches within woodlands, open barrens and places with shallow soil and sparse vegetation.

Range

Historically, mottled duskywings could be found throughout the eastern and central U.S. and parts of south-central Canada. Unfortunately, their populations have plummeted to the point where they may have disappeared from many U.S. states in their core range. In Canada, these butterflies once extended into southwestern Quebec, southern Ontario and southeastern Manitoba. However, mottled duskywings have not been seen in Quebec since the 1950s, and in Ontario, they are only found in small, isolated populations. In Manitoba, they are limited to a small area of pine woodland in the southeast.

Biology

The mottled duskywing follows two distinct life patterns depending on location. In central Ontario, the butterfly produces just one generation per year. In warmer southern areas like Pinery Provincial Park and Norfolk County, two generations emerge annually, one in May, another in July. Females deposit single eggs directly onto New Jersey tea (Ceanothus americanus) or prairie redroot (Ceanothus herbaceus) plants, typically on new growth or flower buds. The eggs hatch within a few days and, once hatched, the caterpillars are independent and immediately begin constructing shelters from woven silk around leaves. They grow for about 2 months and if it is warm enough they will pupate in a cocoon for 2 to 4 weeks (if too cold, they overwinter as mature larvae before pupating) then emerge as an adult. Adult mottled duskywings live for about 2 to 3 weeks in the wild.

Males and females carry “scent scales,” which contain pheromones for attracting the opposite sex. Males are often found “puddling” — sipping water from moist soil to get salt and essential minerals. During mating, those nutrients are transferred to the female through the male’s sperm, which in turn improve the health of the female’s eggs.

Threats

Habitat destruction and fragmentation caused by human development ranks as a primary threat to the mottled duskywing. Meanwhile, the plants these butterflies depend on are being eaten by deer and crowded out by invasive species. Spraying to control spongy moth populations is also taking a toll on the mottled duskywing.

Recovery

Recommended Recovery Actions

The Ontario Recovery Strategy for mottled duskywing calls for a number of conservation measures. These include mapping suitable habitat, protecting and managing habitat, analyzing the viability of current populations, and identifying the potential for augmenting existing populations, reintroducing populations to historical sites or assisting the colonization of new sites.

What we are doing

Find out how we are currently saving other native pollinators, including mottled duskywing, and how you can make a difference.

Visit the project page

What you can do

Anyone with land in suitable oak savanna, pine woodland, or prairie habitat can plant New Jersey tea. Supporting organizations working on habitat restoration directly aids the butterfly. If you encounter a mottled duskywing, photograph and report it to your provincial wildlife agency. Every sighting contributes to monitoring efforts.

FAQs

A: Habitat loss is the dominant driver. Mottled duskywings depend on disturbance-maintained ecosystems; landscapes that historically burned periodically and stayed open and sunny. When European settlement suppressed wildfires, forests began closing over oak savannas and prairies. Without regular disturbance, New Jersey tea cannot compete with shade-tolerant trees, and the butterflies disappear. Agricultural conversion and urban development have accelerated the decline, fragmenting populations into isolated pockets.

A: Getting captive females to lay eggs can be challenging. Females sometimes lack sufficient motivation or encounter conditions that don’t trigger oviposition behaviour. 

A: The Ontario Butterfly Species at Risk Recovery Team tests different approaches. They’ve released caterpillars, pupae, and adult butterflies at different sites within Pinery to determine which life stage works best. Early-stage releases (caterpillars and pupae) have the advantage of allowing butterflies to acclimate, select their own pupation sites, and choose preferred feeding and laying areas. Adult releases establish breeding populations quickly. Results show that all three approaches can work, depending on conditions.

A: The Pinery monitoring team uses “distance sampling” surveys. They walk a series of parallel lines through habitat where host plants are abundant, counting and recording the distance at which they first spot each duskywing. This technique provides population estimates without the intensive effort of marking and recapturing individual butterflies. They also note whether they observe mating, egg-laying, and presence of caterpillars; all signs of reproductive success.