Plebejus idas nabokovi
Northern blue
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Photo by David Cuthrell 

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Key Characteristics

The Northern blue is a small silvery butterfly with a wingspan of 0.9-1.25 inches (2.2-3.2 cm). The dorsal surface is silvery blue in males with a narrow dark border and white fringe; in females it is gray brown near the anterior and outer edges of the wings with areas of blue toward the bases and posterior edges of the wings. The hindwing of the female has a row of dark spots, sometimes orange, along the outer edge. The ventral surface of both sexes is pearly gray to white with several rows of small black spots on the inner portions of both wings and a row of metallic blue-green, orange, and black spots just inside the outer margin of both wings, becoming less pronounced in the forewing.

Status and Rank

  • State Status: T
  • State Rank: S2
  • Global Rank: G5TU

Occurrences

County NameNumber of OccurrencesYear Last Observed
Alger12009
Dickinson11980
Keweenaw21986
Marquette42011
Schoolcraft11995
Distribution map for Plebejus idas nabokovi

Updated 7/21/2017. Information is summarized from MNFI's database of rare species and community occurrences. Data may not reflect true distribution since much of the state has not been thoroughly surveyed.

Habitat

The Northern blue is found in open sandy or rocky habitats, such as in patches of open habitat in spruce (Picea glauca) forests, along rights-of-way, and near rock outcroppings that support the larval host plant, dwarf bilberry (Vaccinium cespitosum). One of the best known populations occurs on a nearly flat, sandy plain adjacent to a railroad track. This site is characterized as scattered shrubs (e.g. Salix) with a ground cover which is typical of open, dry, sandy areas including bracken fern (Pteridium aqulinum), hair grass (Deschampsia flexuosa), and reindeer moss (Cladina rangiferina).

Specific Habitat Needs

Host plant needed in Dry northern forest, Oak-pine barrens, Pine barrens

Natural Community Types

Methodology

For each species, lists of natural communities were derived from review of the nearly 6,500 element occurrences in the MNFI database, in addition to herbarium label data for some taxa. In most cases, at least one specimen record exists for each listed natural community. For certain taxa, especially poorly collected or extirpated species of prairie and savanna habitats, natural community lists were derived from inferences from collection sites and habitat preferences in immediately adjacent states (particularly Indiana and Illinois). Natural communities are not listed for those species documented only from altered or ruderal habitats in Michigan, especially for taxa that occur in a variety of habitats outside of the state.

Natural communities are not listed in order of frequency of occurrence, but are rather derived from the full set of natural communities, organized by Ecological Group. In many cases, the general habitat descriptions should provide greater clarity and direction to the surveyor. In future versions of the Rare Species Explorer, we hope to incorporate natural community fidelity ranks for each taxon.

Management

Protection of existing populations and their habitat should be the first conservation priority. Habitat enhancement by maintaining existing openings and creating additional openings in a matrix on the landscape would maintain different successional stages, providing patches of new habitat and ready sources of colonizers. Historically, fire was important in maintaining open habitat patches. To some extent, railroads assisted that process for many years, through both accidental fires and prescribed burns along railroad rights-of-way. The Northern blue is fire sensitive at all stages in its life, so any burn management program should include subunits that are managed on a rotating basis, always leaving significant portions of the habitat, including both dwarf bilberry and nectar sources, unburned. Any management should be carefully monitored to determine its affect on both the butterfly and dwarf bilberry.

Active Period

Flight from first week of June to fourth week of July

Survey Methods

Larvae are present once foliage emerges in the spring until mid-June. In Michigan, adults of this species have been observed from early to mid-June to late July. The best way to survey for this species is to conduct visual surveys while meandering through habitat looking for flowers and nectaring adult butterflies. A pair of close focusing binoculars may be used to help locate individuals. Most butterfly surveys should be conducted on warm, sunny days with little to no wind.

Page Citation

Michigan Natural Features Inventory. 2007. Rare Species Explorer (Web Application). Available online at http://mnfi.anr.msu.edu/explorer [Accessed Nov 22, 2017]

More Information

See MNFI Species Abstract

References

Survey References

Technical References

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