Rare Species Guide

  Basis for Listing

The Persius Duskywing (Erynnis persius persius), also known as the Hairy Duskywing, comprises several subspecies, including the eastern Erynnis persius persius and one or more western ones.” The eastern subspecies is limited to a narrow zone from New England south to Virginia and westward through the Great Lakes to southeastern Minnesota. Collectively, the other subspecies have a wide distribution in western North America (Layberry et al. 1998; Lotts and Naberhaus 2017). Only the eastern subspecies occurs in Minnesota, and all references hereinafter to Persius Duskywing refer to E. persius persius. The Persius Duskywing occurs in open sandy savannas and barrens where its larval host plants, primarily wild lupine (Lupinus perennis) but sometimes also yellow wild indigo (Baptisia tinctoria), are common. It is now rare throughout its range primarily because of destruction of the specialized habitat of its larval host plants (NatureServe 2025). This is the same habitat required by the federally threatened Karner Blue (Plebejus melissa samuelis), which is also the eastern subspecies of a species widely distributed in western North America.

The Persius Duskywing has only been recorded from two sites in Minnesota, both in Winona County (The Blufflands Subsection). One site is represented by a single specimen collected in 1951; at the other site, the skipper was first observed in 1974 and has been observed there several times in subsequent years, indicating that it supports a resident population. Observations to date indicate that this colony is very small (Cuthrell 1990; R. Huber, pers. comm.). A Minnesota DNR survey of all known sites in Minnesota having suitable habitat did not find this species elsewhere (Cuthrell 1990), nor have other experienced lepidopterists who have visited these sites. Given its extreme rarity in the state, the Persius Duskywing was listed as an endangered species in Minnesota in 1996.

  Description

The Persius Duskywing is one of several very similar looking skippers that occur in Minnesota. Like the other duskywings, it is a small butterfly (forewing length 1.1-1.5 cm [0.4-0.6 in.] from base to apex) with rounded wings, a moderately robust body, and antennae that end in a slender curved or hooked club. It is dark blackish brown above, slightly lighter below. Males have a very subtle gray mottling on the forewings above, which is more pronounced in females. There is a short row of very small translucent spots forming a line perpendicular to the leading edge of the forewing out near the tip in both sexes. Females usually have a few additional larger spots in the more central part of the wing, but these are reduced or absent in males. These skippers frequently alight on the ground, where they hold their wings spread flat or even pressed against the surface.

The Persius Duskywing resembles several other duskywing species in Minnesota. The Dreamy Duskywing (E. icelus) is smaller, the upper surface of the forewings is much more strongly mottled, and there are no translucent spots. The Sleepy Duskywing (E. brizo) is browner and lacks the gray dusting on the upper forewings. It also lacks translucent spots. Juvenal's Duskywing (E. juvenalis) is larger than the Persius, and the translucent spots on the forewing are usually prominent. Juvenal's also has two conspicuous pale spots near the apex of the hindwing beneath. Both sexes of the Mottled Duskywing (E. martialis) have a very mottled appearance on both hind and forewings above, and fresh individuals have a purplish sheen. Distinguishing the Persius Duskywing from the Wild Indigo Duskywing (E. baptisiae) and the Columbine Duskywing (E. lucilius) is especially difficult, and records without voucher specimens are unreliable. In the Persius Duskywing, the inner margins of the little spots near the apex of the forewing form a nearly straight line, whereas they are more irregularly arranged in the other two species. The Persius Duskywing male is distinguished from all other duskywing males in Minnesota by the presence of long white or gray hair-like scales that stand above the flat scales on the upper side of the forewings. These wear off, and reliable determination of worn specimens requires examination of genitalic characters. Two other similar-looking skippers are the Northern Cloudywing (Cecropterus pylades) and Southern Cloudywing (Cecropterus bathyllus). These have very little grayish mottling of the forewings above and have a number of translucent white spots on the forewings, usually quite large in the Southern Cloudywing. The hindwing below has a distinct banded pattern, not the light flecks the Persius Duskywing has. They also tend to hold their wings at a more erect angle when resting or feeding.

  Habitat

Minnesota's only confirmed population of the Persius Duskywing is in a mosaic of oak woodland and savanna or barrens on sand where wild blue lupine is common. This is similar to the habitat reported for Wisconsin and Michigan occurrences (Swengel and Swengel 1997; Nielsen 1999).

  Biology / Life History

The Persius Duskywing has a single annual generation. The adult flight period is in May and early June in Minnesota. In Michigan, mature larvae hibernate and pupate in early spring (Nielsen 1999).

Scudder (1864) reported willow (Salix spp.) and poplar (Populus spp.) to be larval host plants in his original description of this species, but all recent work strongly indicates that wild lupine is the principal larval host, with yellow wild indigo (possibly other wild indigo species) being used occasionally in some other states. These plants are members of the pea family (Fabaceae), as are all larval hosts for the western subspecies (Scott 1986). Larvae share the habit of other members of the same genus of tying leaves of the host plant together with silk to form a simple shelter in which they rest between bouts of feeding. Adults have been observed taking nectar from a variety of plants (Nielsen 1999), suggesting that they will visit any nectar-producing flowers that are available.

Males seek receptive females primarily by perching on low vegetation or bare spots and pursuing any passing insect that might be a female Persius Duskywing. The courtship and mating behavior of the eastern subspecies does not appear to have been described. Nothing is known about the dispersal behavior of mated females.

  Conservation / Management

The apparent restriction to a single small population in Minnesota is the primary threat facing the Persius Duskywing in the state. Such a small, isolated colony is at high risk of extirpation resulting from both natural events (such as severe drought or hailstorms) and human caused ones (such as insecticide application) as well as from the vagaries of normal population processes (for example, by chance all adults in one generation are males). Loss of genetic diversity in a small population is another possible threat. The Minnesota colony is at least 80 km (50 mi.) from the nearest known occurrences in Wisconsin (Eau Claire and Jackson counties), making it unlikely that immigration from the Wisconsin population will maintain genetic diversity.

The possible fragmentation of this small colony into even smaller units, confined to the separate patches of suitable habitat, aggravates the risk of extirpation. Fire suppression has allowed the original oak scrub and woodland matrix to grow up into dense woodland and forest, encroaching on open habitat and impeding butterfly movement among the shrunken open patches. The Persius Duskywing is probably highly susceptible to fire, as all immature stages are in the lupine foliage. Prescribed burn units should be configured to always allow for butterfly survival in unburned parts of each habitat patch, and rotation should allow for population recovery between burns (this would be longer than for the Karner Blue, because the Karner Blue has two generations per season). An intensive survey to determine the distribution of the Persius Duskywing among the habitat patches and its abundance is needed to design an appropriate fire management regime. Mechanical clearing is an option where fire would be risky, but the long-term suitability of areas managed exclusively with mechanical clearing is unknown. Opening up woodland and forest between patches to provide greater connectivity can be done at little or no risk to the butterflies.

The oak-dominated woodlands and forests in the area where the Persius Duskywing occurs are prime candidates for defoliating outbreaks of the Spongy Moth (Lymantria dispar). Recent efforts to manage Spongy Moth with the toxin derived from the bacterium Bacillus thuringiensis var. kurstaki (Btk) are likely to overlap with Persius Duskywing populations and is probably highly toxic to the species.  It is imperative to keep the application of this product well away from any habitat where the Persius Duskywing occurs.

  Conservation Efforts in Minnesota

All of the known habitat occupied by the Persius Duskywing in Minnesota is within a Wildlife Management Area owned by the Minnesota DNR. Because this area is also critical habitat for the Karner Blue, there is an ongoing research and management effort on behalf of that butterfly that should be equally beneficial for the Persius Duskywing. The need for additional information about the distribution and abundance of the Persius Duskywing within the site has already been noted.

There are few known occurrences in Minnesota of habitat suitable for the Persius Duskywing. These areas were surveyed for the Karner Blue in 1990 by the Minnesota DNR (Cuthrell 1990), and the Persius Duskywing was also included as a target species by the surveyor. The Persius Duskywing was only found at the one location with a resident population. The other sites have also been visited one or more times by other experienced lepidopterists with no new populations found.

  Authors/Revisions

Robert P. Dana, Ph.D. (MNDNR), 2025
(Note: all content ©MNDNR)

  References and Additional Information

Cuthrell, D. L. 1990. Status of the Karner Blue Butterfly, Lycaeides melissa samuelis Nabokov, in Minnesota 1990. Report submitted to the Nongame Wildlife Program, Minnesota Department of Natural Resources. 44 pp. + appendix.

Layberry, R. A., P. W. Hall, and J. D. LaFontaine. 1998. The butterflies of Canada. University of Toronto Press, Toronto, Ontario. 280 pp. + color plates.

NatureServe. 2008. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.0. NatureServe, Arlington, Virginia. . Accessed 3 June 2008.

Nielsen, M. C. 1999. Michigan butterflies and skippers: a field guide and reference. Michigan State University Extension, East Lansing, Michigan. 248 pp.

Opler, P. A., H. Pavulaan, R. E. Stanford, and M. Pogue, coordinators. 2006. Butterflies and moths of North America: Persius Duskywing (Erynnis persius ). Bozeman, Montana: NBII Mountain Prairie Information Node. . Accessed 19 July 2006.

Scott, J. A. 1986. The butterflies of North America: a natural history and field guide. Stanford University Press, Stanford, California. 583 pp.

Scudder, S. H. 1864. A list of the butterflies of New England. Proceedings of the Essex Institute 3:161-179.

Swengel, A. B., and S. R. Swengel. 1997. Co-occurrence of prairie and barrens butterflies: applications to ecosystem conservation. Journal of Insect Conservation 1:131-144.