Erynnis martialis – Mottled Duskywing Butterfly

Habitat:
MODU populations will only occur where their host plant grows. Their host plant(s) prefers a dry habitat with sparse vegetation. In Ontario, this may be open barrens, sandy patches in woodlands, the rare ecosystems of Ontario – oak woodlands, pin woodlands, tallgrass prairies – and alvars. Alvars are limestone areas with shallow dry soil (clay or sandy), having sparse vegetation of early successional grass, shrub and wildflower species. Neither C. americanus nor C. herbaceous are tolerant of closed canopies.

Behaviour:
While some skippers are migratory, E. martialis is a non-migratory species that uses their habitat, and specifically their host plant for all stages of life. Their flight is low to the ground in a fast, erratic pattern. By comparison with other duskywings, MODU are considered sedentary and less mobile. They are said to have limited dispersal ability.

Larvae build silk-lined leaf-nests on their food plants. Leaves are cut or folded or several are pulled together. With nocturnal feeding habits, they venture out at night to feed on leaves, or shorten their trip by cutting leaf sections to take back to their shelter for consumption later.

“Nectaring” is the act of feeding from floral nectar sources. Nectar is an essential adult food, rich in sugar. Adult MODUs tend to prefer sites with partial shade, abundant nectar sources and ample larval food plant, C. americanus, supply.

During mating season, the males will gather and patrol on local hilltops to attract and compete for females. Males can be seen “puddling” – sipping water from moist soil – in the company of other duskywing species. The salt and essential minerals gathered from soil water are incorporated into the male’s sperm and passed onto the female and her eggs when mating. These nutrients improve the viability of her eggs.

Life Cycle:
After mating occurs and the female has been fertilized, she will deposit her eggs on the leaves of a host, C. americanus or C. herbaceus, plant. Her eggs are hemispherical, with fine sculpturing or marked with vertical ridges. They begin pale green in colour, but quickly turn to pink.

Larvae (caterpillars) hatch only days after egg-laying. They are stout, sluggish, pale green, smooth or covered with fine bumps, short hairs or tubercles. Their large heads are dark with small patches of red, orange or yellow. The prothorax is narrow, giving the appearance of having a neck. They are cylindrical in shape, sometimes tapered at both ends. The last segments often divide into two “tails”. At maturity, they can be 25 mm long. The larva creates a day shelter for itself by stitching leaves together with silk. At night, the caterpillar leaves the shelter to feed.

A mature larva spins a cocoon no more than 1-2 cm beneath the leaf litter at the base of its food plant. In the extreme part of southwestern Ontario, it will pupate (form a chrysalis) and emerge a few weeks later, unless the weather is unfavourable. In this case, or if its habitat is further north, it will go into diapause (a state of dormancy) and overwinter.

Exposure to early spring solar warmth encourages pupation. Emergence occurs mid-May to early-June, depending on northerly/southerly location within the range. The chrysalis, or pupa, vary from dark green to brown. Round and smooth, it has a squared off head, a noticeable tongue and a tail that comes to a tufted point.

Adults are on the wing by mid May to late June. In extreme southwestern Ontario, the female may lay a second brood, to hatch early July and take flight mid-July to late August.

Threats:
The main threat to Mottled Duskywing is destruction of habitat, including habitat fragmentation, due to various forms of human development. These include changes by design, such as the planting of jack pine; pesticide use, including spraying for gypsy moth control; flooding; and, introduction of invasive species, such as Dog Strangling Vine. All being direct threats to MODU’s host plant, C. americanus (New Jersey Tea), they present real and present dangers to this butterfly species.

Also threatening MODU’s host plant are natural habitat changes resulting from natural succession, canopy closure and deer browsing. Disturbance such as fire, both natural and controlled burns, can cause direct mortality of individual butterflies; however, this kind of disturbance will also serve to maintain suitable habitat conditions. The woody plants get burned off, clearing the way and open the canopy for fire tolerant New Jersey Tea to flourish.

Presently, there are only small, scattered populations of Erynnis martialis (Mottled Duskywing) in Ontario. Similar duskywings, Karner Blue, Frosted Elfin and Eastern Persium are mostly gone from Ontario and Canada at large. As we speak, The Ontario Butterfly Species at Risk Recovery Team is working to reintroduce and establish a self-sustaining population of Mottled Duskywing butterfly in the oak savanna habitat of Pinery Provincial Park (on the southern shore of Lake Huron).

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