Northern blue butterfly (Plebejus idas)

Also known as: Idas blue, Nabokov’s blue, northern blue
Synonyms: Lycaeides argyrognomon nabokovi, Lycaeides idas
GenusPlebejus (1)
SizeWingspan: 2.2 - 3.8 cm (2) (3)

The northern blue butterfly has yet to be classified by the IUCN.

The northern blue butterfly (Plebejus idas) is a small North American butterfly with bright silvery-blue to purplish-blue wings, outlined with a narrow dark border and a white fringe (2) (3) (4) (5). The female northern blue butterfly is more variable in colour than the male, generally being grey-brown above, with the blue colouration confined to the bases and rear edges of the wings (2) (4) (5). The hind wing of the female has a row of dark, sometimes orange spots along its outer edges (2) (5).

In both the male and female northern blue butterfly, the undersides of the wings are dull greyish to white, with several rows of small, black spots. There is also a row of orange crescents and metallic blue and black spots near the wing margins, particularly on the hind wings (2) (4) (5). A thin black line around the wing margins expands into triangles or small dots at the ends of the wing veins (2) (3).

The northern blue butterfly is somewhat variable in appearance across its range (3), and a number of subspecies are recognised (1) (4).

The caterpillar of the northern blue butterfly is shaped like a slug, and is green with a dark line on the upper surface and light yellow stripes along the sides. Its head is small and black (4).

The primary distinguishing feature of the northern blue butterfly, which separates it from most other related species, is the combination of orange spots on the underside of the wings and the lack of a ‘tail’ on the hind wings (2). The northern blue butterfly is very similar in appearance to the Melissa blue (Plebejus melissa), but usually has less orange on the underside of the wings. The female Melissa blue also has an orange band on the upper surfaces of the wings. The males of the two species are more difficult to tell apart (4) (5).

The northern blue butterfly ranges from Nova Scotia in Canada, south to the Great Lakes region of the United States, including Minnesota, Wisconsin and Michigan (2) (3) (4) (5). Its range also extends west across Canada to Alaska, and south into the Pacific Northwest region of the United States, as far as California, Idaho and Colorado (3) (4) (5).

Open sandy, rocky or savanna-like landscapes with a ground cover of dwarf bilberry (Vaccinium caespitosum) are the dominant habitats of the northern blue butterfly. This species commonly occurs in openings in pine forests, and is often associated with railroads, roadsides and rock outcrops (2) (4) (5).

The northern blue butterfly produces a single brood of young each year. Adult northern blue butterflies emerge in early June to July, with the males typically emerging before the females and flying within a metre of the ground as they patrol for a mate (2) (3) (4) (5). Mating usually occurs close to patches of dwarf bilberry (Vaccinium caespitosum), a small shrub which serves as a host plant for the northern blue butterfly’s larvae (2) (4) (5).

After mating, the female northern blue butterfly lays eggs singly on the stems of the host plant or on nearby vegetation. The eggs of this species remain dormant over the winter, not hatching until the following spring, when the caterpillar begins feeding on the host plant (2) (3) (4) (5). In some areas, the northern blue butterfly has also been observed using other species as host plants for its caterpillars, including black crowberry (Empetrum nigrum), Labrador tea (Ledum groenlandicum) and sheep laurel (Kalmia angustifolia) (2).

The caterpillars and pupae of the northern blue butterfly are tended by Formica ants, which probably help to protect the caterpillars from predators and parasitoids (4) (5). The caterpillar has specialised organs that produce a secretion that the ants feed upon, and probably also mimics ant pheromones to further manipulate the ants’ behaviour (5). The northern blue butterfly caterpillar usually pupates by mid-June to early July, forming a green pupa that gradually turns yellow and then black before the adult emerges about ten days later (4) (5).

The adult northern blue butterfly feeds on the nectar of a variety of native and non-native flowers (2) (3) (4) (5), but is nearly always found near to patches of the caterpillar’s host plant (5). Although the adult may live for up to three weeks after emerging, the average adult survival is usually no more than a week (5).

Major threats to the northern blue butterfly include the encroachment of woody vegetation into open areas populated with dwarf bilberry shrubs, as well as forestry practices that eliminate its host plant or affect forest openings (4) (5). The importance of fire for the northern blue butterfly is uncertain, as fire preserves open dry habitat, but is directly related to dwarf bilberry and butterfly mortality (2) (4) (5). Vehicle traffic and mortality due to parasitoids also negatively affect the northern blue butterfly’s survival (4).

At least one subspecies of the northern blue butterfly, the lotis blue butterfly (Plebejus idas lotis), is highly threatened. This subspecies is probably naturally rare, but is now known from only one small region in California (3) (4), having lost its host plant due to vegetation changes caused by human disturbance (3). Some fear that the lotis blue butterfly may already be extinct (4).

Conservation efforts for the northern blue butterfly should target the management of this species’ host plants, specifically the dwarf bilberry, and deter the growth of woody vegetation (2) (4) (6). It will be important to adequately protect the northern blue butterfly’s habitat, and also to enhance it by maintaining existing open areas and creating new ones (2) (4).

Additional monitoring and field surveys have also been suggested to aid conservation efforts for this species, as it would be beneficial to learn more about the northern blue butterfly’s biology and ecology (2) (3) (4) (6). Prescribed burns coupled with butterfly monitoring have been suggested for long-term conservation efforts, although burns needs to be used with caution as the northern blue butterfly itself is vulnerable to fire (2) (4) (5).

Find out more about the northern blue butterfly and its conservation:

More information on butterfly conservation in North America:

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:

  1. Integrated Taxonomic Information System (ITIS) (September, 2011)
  2. Cuthrell, D.L. (2001) Special Animal Abstract for Lycaeides idas nabokovi (Northern Blue Butterfly). Michigan Natural Features Inventory, Lansing, Michigan. Available at:
  3. Opler, P.A., Lotts, K. and Naberhaus, T. (2011) Northern blue, Plebejus idas. In: Butterflies and Moths of North America. Big Sky Institute, Bozeman, Massachusetts. Available at:
  4. Wolf, A.T and Brzeskiewicz, M. (2002) Conservation Assessment for Northern Blue Butterfly - Plebejus (Lycaeides) idas nabokovi (Masters) and Dwarf Bilberry - Vaccinium caespitosum (Michx). USDA Forest Service, Eastern Region, Milwaukee, Wisconsin. Available at:
  5. Minnesota Department of Natural Resources: Species Profile - Lycaeides idas nabokovi, Nabokov’s blue (July, 2011)
  6. Wisconsin Department of Natural Resources (2011) Protocol for Incidental Take Authorization: Northern Blue Butterfly (Lycaeides idas nabokovi). Wisconsin Department of Natural Resources, Madison, Wisconsin. Available at: