New York Natural Heritage Program
Mottled Duskywing
Erynnis martialis (Scudder, [1870])

General Description [-]
oth sexes are brown dorsally with black patches, lending the butterflies a strongly mottled or banded appearance (Opler and Krizek, 1984). Above and below-light brown with lavender cast; very strong contrasting dark patches on all wings so it appears almost banded; tiny glossy spots on fore wing; brown fringes (Pyle, 1981). Spring or 1st brood phenotype is smaller (male forewing 1.8-1.9 cm) and lighter (with more white scaling) than summer or 2nd brood phenotype (male fore wing 2.0-2.1 cm); gray hairs of male dorsal fore wing concentrated on distal 3rd of wing; hyaline spots small and usually absent in fore wing space cu2-2a in both sexes; ventral hind wing lacks subapical white spots (Scott, 1986). Mature larva-light green with white specks and covered with short hair; head is red, yellow or orange pattern. Eggs-pale green, turning pink before hatching (Pyle, 1981).

Identifying Characteristics [-]
This species has been commonly misidentified in the past in other states. However, this is less of a problem in New York because females of the Horace's Duskywing (Erynnis horatius), a similar species, appear to be the main source of confusion and this species is not widespread in New York.

Characters Most Useful for Identification [-]
A small, very bright, and contrasting duskywing. The purplish sheen is diagnostic when obvious. Note the narrow sharply delineated hindwing band. The size can be unreliable because small females of Horace's Duskywing (Erynnis horatius) are very similar. This species can be tentatively identified from Brock and Kaufman (2003) or Glassberg (1993, 1999), but it should be verified by an expert based on a specimen or several diagnostic images. Some images may leave room for doubt, however.

Best Life Stage for Proper Identification [-]
The larval stage is perhaps the easiest to identify. Any larva that can be determined to be a skipper and is found living in a folded leaf of and eating the same plant, Ceanothus spp., will be this species. However, it will usually be found in the adult stage.

Diet [-]
The larval foodplants are species of Ceanothus, primarily New Jersey Tea (Ceanothus americanus), but Prairie Redroot (Ceanothus herbaceus) is the foodplant in Clinton County. The adults sip moist soil and take nectar from a variety of flowers, perhaps most often those of Ceanothus spp. when flowering coincides with the second brood.
Mottled Duskywing Images
click to enlarge
The Best Time to See
Shapiro (1974) thought there to be one brood (generation) from mid-June to 21 August in the Ithaca area. However, this length of time is long enough to represent two broods and there have been two broods documented in all adjacent states and in Ontario, with the dates of these broods occurring about mid-May and June and late July to mid-August in most localities. The Clinton County records are in early to mid-June and the Jefferson County record from Tom Fiore and Kristine Wallstrom is 13 May 2004. Each brood probably occurs over a period of less than a month during most years, and the Mottled Duskywing is not likely to be found reliably in late June or early July, despite a few records during this period of time. The two broods overlap the Karner Blue (Plebejus melissa samuelis), but the first brood starts earlier, occasionally even in late April. The Mottled Duskywing is probably most reliably found from mid to late May and the last two weeks of July.
Reproducing Larvae present and active
The time of year you would expect to find Mottled Duskywing reproducing (blue shading) and larvae present and active (orange shading) in New York.