Erynnis martialis

Description

The Mottled Duskywing (Erynnis martialis) is a medium-sized butterfly in the skipper family (Hesperiidae) with a wingspan of 25-42 mm. Adults are dark grey with yellow-brown spots on the hindwings that create a distinctive mottled pattern — hence the common name. Freshly emerged adults have a delicate purplish iridescence that fades with age. The species flies low to the ground in a fast, erratic pattern characteristic of skippers, making field identification challenging.

The Mottled Duskywing is listed as Endangered under Ontario's Endangered Species Act, 2007, and has been on the Species at Risk in Ontario List since June 2014. Globally, NatureServe ranks the species as Vulnerable (G3). It is a species of special concern and believed extirpated in Connecticut, and populations across its range have declined significantly due to habitat loss and fragmentation.

Lifecycle

Two generations are produced per year in southern Ontario. Adult females deposit eggs exclusively on the leaves of Ceanothus host plants — primarily New Jersey Tea (Ceanothus americanus) and Prairie Redroot (Ceanothus herbaceus). Upon hatching, larvae construct silk leaf-nests, folding and securing host plant leaves into protective shelters where they feed and rest.

Mature larvae overwinter in the leaf litter at the base of the host plant — a critical life stage that makes the species vulnerable to disturbance of the ground layer during winter months. The first adult brood emerges from mid-May to late June. The second brood matures in early July and flies from mid-July through late August. In mating season, male Mottled Duskywings congregate on local hilltops to compete for females — a behaviour known as hilltopping that is common among Hesperiidae.

Ecology

The Mottled Duskywing is an obligate feeder on Ceanothus species throughout its larval stage. This tight ecological dependency means the butterfly's fate is inextricably linked to the health and extent of New Jersey Tea populations. In Ontario, it will only deposit eggs on Ceanothus americanus and C. herbaceus. Adults nectar on a variety of flowers including bush houstonia (Houstonia), gromwell (Lithospermum), and hoary vervain (Verbena stricta).

The primary threats to the species in Ontario are habitat loss and degradation. The oak savanna, alvar, and dry barrens habitats where Ceanothus thrives have been reduced to a tiny fraction of their historic extent by urban development, agriculture, and fire suppression. Spongy Moth control programs using broad-spectrum insecticides pose an additional direct threat — the same issue affecting Northern Oak Hairstreak and other oak-savanna Lepidoptera.

The species is the subject of active recovery efforts including habitat restoration and a reintroduction program at Pinery Provincial Park. Other butterfly species with similar habitat requirements — Karner Blue, Frosted Elfin, and Eastern Persius Duskywing — have already disappeared from Ontario, making the Mottled Duskywing's continued presence particularly significant.

Host Plants

Larvae feed exclusively on Ceanothus species in the Rhamnaceae:

• New Jersey Tea (Ceanothus americanus) — primary Ontario host
• Prairie Redroot (Ceanothus herbaceus) — secondary Ontario host

Habitat

The Mottled Duskywing occupies some of Ontario's rarest ecosystems: dry oak savannas, pine woodlands, alvars (limestone barrens with shallow soil and sparse vegetation), and open sandy barrens. These habitats share common features — well-drained, nutrient-poor soils, sparse tree cover, and the presence of Ceanothus host plants. Scattered populations occur throughout southern Ontario, with recent documentation from Burlington, Oakville, and Marmora (east of Peterborough). Several documented sites are within protected areas including provincial parks and conservation lands.