Karner Blue (Plebejus melissa samuelis)

In this guide

1. Description and identification
2. Life cycle: egg, caterpillar, chrysalis and adult
3. Where the Karner blue butterfly lives
4. Host plants and diet
5. Behavior: ants, flight and conservation
6. Similar butterflies and how to tell them apart
7. Quick facts
8. Did you know?
9. Pictures
10. Frequently asked questions

Description and identification

The Karner blue is a subspecies of the melissa blue, placed in the subfamily Polyommatinae of the gossamer-winged butterfly family. Like the rest of that family it is small, delicately built and covered in scales that scatter light rather than absorb it, which is why a male looks metallic in sunshine and dull grey in shadow. It is one of the smallest butterflies in eastern North America, and in the field it registers as little more than a pale blue spark low over the lupine.

Adult butterfly

• Wingspan: 0.9–1.3 in (22–32 mm), roughly the size of a US quarter with the wings spread.
• Male upperside: a bright silvery violet-blue over the whole wing surface, bordered by a narrow black line and edged with a clean white fringe. There are no orange marks above.
• Female upperside: quite different — grey-brown over most of the wing, washed with blue towards the body, and with a band of orange crescents inside the dark margin of the hindwing, sometimes continued faintly onto the forewing.
• Underside: the diagnostic surface, and identical in both sexes. It is a soft silvery grey, scattered with round black spots each ringed in white, and around the outer edge of the hindwing runs a continuous band of orange crescents, each one capped on its outer side by a small patch of iridescent blue-green or silver scales.
• Body: slim, furry-looking and grey-blue, with short black-and-white banded antennae and dark eyes.
• Sexes: instantly separable from above, indistinguishable from below. The blue male and the brown-and-orange female are so unlike each other that early collectors sometimes catalogued them separately.

Fresh specimens are noticeably brighter than worn ones; by the end of a brood the males have faded towards silvery grey and the white fringe is often chipped. There is no seasonal form, but second-brood adults average slightly larger than the spring generation.

How to identify a Karner blue in the field

Three things together make the identification. First, the habitat: this butterfly is almost never seen away from sandy savanna, barrens or oak openings with wild lupine growing in them. Second, the size and flight — a very small butterfly with a weak, low, fluttering flight that seldom rises above knee height and seldom travels far. Third, the underside band, which needs a close look at a settled insect: grey ground, black spots in white rings, and an unbroken row of orange crescents tipped with metallic scales. The eastern tailed-blue is the commonest source of confusion, but it has a short hair-like tail on each hindwing, which the Karner blue never has, and only one or two orange spots rather than a full band.

Life cycle: egg, caterpillar, chrysalis and adult

The Karner blue is double-brooded, and the timetable is tied precisely to the growth of wild lupine. Eggs laid in late summer sit out the whole winter and hatch in April, the first adults fly from late May into June, their offspring produce a second and larger flight in late July and August, and it is the eggs of that second brood that overwinter. Two generations a year sounds like safety, but because both depend on the same plant in the same patch of sand, a single bad season can wipe out a colony.

Eggs

A female lays her eggs singly, usually on a lupine stem, on the underside of a leaf, or on dead plant material and litter directly beneath the plant. Each egg is under 1 mm across, pale greenish-white, flattened like a tiny turban and covered with a fine raised network, which is the standard shape in this family. Spring-brood eggs hatch within about a week. Summer-brood eggs go into diapause and lie in the litter through frost, snow and thaw for seven or eight months, hatching only when the new lupine shoots appear in April.

Caterpillar

The larva is shaped like a small flattened slug rather than a cylinder, another family trait. It is a plain, slightly translucent green with a darker line down the back, a paler stripe along each side and a coat of very short white hairs that gives it a velvety look; the head is black and tucked out of sight beneath the body. It grows to about 0.5 in (13 mm) over roughly three to four weeks. A Karner blue caterpillar grazes the soft tissue from the underside of a lupine leaflet, leaving the upper skin as a translucent window, and it is so exactly the colour of the leaf that the feeding damage is usually spotted first. Larvae of most instars carry a gland on the back that produces a sugary secretion, and ants of several genera attend them constantly to collect it, driving off predatory bugs and parasitic wasps in return.

Chrysalis

When it is fully fed the caterpillar leaves the plant and pupates in the leaf litter, in a crack in the sand or among the lower stems of nearby vegetation. The chrysalis is small, about 0.3 in (8–9 mm), smooth, rounded and pale green, sometimes yellowing before the adult is ready. Ants often continue to attend it. The pupal stage lasts 8 to 11 days in the summer generation, and the adult works its way up out of the litter before expanding its wings.

Adult

Adult Karner blues are short-lived even by the standards of small butterflies: three to five days is normal, and a fortnight is exceptional. Everything is therefore compressed. Males emerge a day or two before females, patrol constantly, and mating usually happens within hours of a female's emergence. A female may lay several dozen eggs in her few days on the wing. Our guide to how long butterflies live explains why such brief adult lives are common among the blues, whose real growing is done in the larval stage.

Where the Karner blue butterfly lives

The Karner blue is restricted to a narrow belt of the northern United States, and it survives today in scattered colonies in Wisconsin, Michigan, Minnesota, Indiana, Ohio, New York and New Hampshire. Wisconsin holds by far the largest remaining population, spread across the central sand plains and managed in partnership with forestry and utility landowners. The butterfly has been lost from Illinois, Iowa, Maine, Massachusetts, Pennsylvania and from Ontario in Canada, and the New Hampshire and Ohio colonies exist because captive-reared stock was released back into restored habitat. Its name comes from Karner, a hamlet in the Albany Pine Bush of New York where the subspecies was first recognised.

The habitat is as narrow as the range. Karner blues need dry sandy soils carrying oak savanna, jack pine and pitch pine barrens, lakeshore dunes or old sand prairie — open ground with scattered trees, where wild blue lupine grows in dappled light rather than in either full shade or baking sun. Such places are naturally maintained by fire and by grazing, and when those stop the shrubs and trees close in, the lupine disappears and the butterfly follows within a few years. Modern colonies frequently survive on substitutes for the old disturbance regime: military training areas, power line corridors, firebreaks and roadside verges that are mown or burned on rotation.

Adults are extremely sedentary. Most individuals spend their whole lives within a few hundred metres of where they emerged, and even a hundred metres of closed woodland or a wide field of crops is enough to isolate one lupine patch from the next. That is why habitat restoration for this species is as much about linking fragments as about creating them.

Host plants and diet

Caterpillar host plant. Wild blue lupine, Lupinus perennis, is the only host plant the Karner blue caterpillar will accept anywhere in its range. No other lupine and no other legume substitutes for it, and garden lupines sold for flower borders are different species that the larvae cannot use. The dependence runs deeper than food: the lupine must be growing in partial shade to stay green and palatable into July, so that the second brood of larvae has soft leaves to eat. Lupine that is stressed by full sun sets seed and dies back early, and a colony can fail even though the plant is still present.

Adult diet. Adults are far less fussy than their caterpillars and take nectar from a wide spread of savanna and barrens flowers. Recorded favourites include butterfly weed, wild bergamot and horsemint, New Jersey tea, blazing star, dogbane, goldenrod, black-eyed Susan and various legumes, and both broods need a good supply of these in flower during their short flight periods. Males also gather at damp sand and mud to take up salts and minerals, which they pass to the female in the spermatophore at mating.

Behavior: ants, flight and conservation

A partnership with ants. The most remarkable thing about this butterfly happens in the larval stage. The caterpillar carries a dorsal nectary organ that oozes a sugary, amino-acid-rich fluid, and ants of several genera — including Formica, Camponotus and Myrmica — harvest it. In exchange the ants attack the small predatory bugs, spiders and parasitic wasps that would otherwise kill the larva. Caterpillars tended by ants survive far better than untended ones, so the health of a Karner blue colony depends not only on lupine but on the ant community living around it. This kind of relationship is common in the gossamer-wings and is one of the reasons the family is so sensitive to habitat change.

Flight. The flight is weak, low and fluttering, rarely more than a metre above the ground, and it stops often. Butterflies rest with the wings closed, showing only the grey underside, and bask early in the day with the wings half open to catch the sun. In cool or windy weather they hardly fly at all, which makes surveying the species a matter of picking the right hour on the right day.

Male behaviour. Males spend most of their brief lives patrolling low over lupine looking for newly emerged females, and they congregate at moist sand or the edges of puddles in numbers that can make a small colony look larger than it is. The general courtship sequence is set out in our guide to how butterflies mate and reproduce; in the Karner blue it is compressed into a matter of minutes, and females usually mate once.

Conservation. The Karner blue was listed as endangered under the US Endangered Species Act in 1992, and NatureServe ranks the subspecies as imperiled, a status well below that of the widespread melissa blue to which it belongs. The causes are habitat loss and habitat succession: sand savanna converted to farmland, housing and plantation forest, and the remaining fragments growing shut for lack of fire. Recovery work now centres on prescribed burning and mowing in rotation, replanting lupine, captive rearing and reintroduction, and joining isolated patches into networks. Several other blues in the same family are in similar trouble, among them the mission blue of the San Francisco hills and the Miami blue of the Florida Keys.

Similar butterflies and how to tell them apart

Quick facts

Did you know?

• The Karner blue was formally described in 1944 by the novelist Vladimir Nabokov, who worked as a lepidopterist at Harvard's Museum of Comparative Zoology and named it Lycaeides melissa samuelis.
• The name comes from Karner, a small settlement in the Albany Pine Bush of New York state. Part of that pine bush is now a protected preserve managed largely for this butterfly.
• Ants are effectively the caterpillar's bodyguards. They milk a sugary secretion from a gland on its back and, in return, drive away the predators and parasites that kill unattended larvae.
• Wild lupine needs partial shade to stay green into midsummer, so paradoxically the butterfly cannot survive in a fully open field or in a closed forest — only in the half-shaded savanna in between.
• Most adults never travel more than a few hundred metres in their lives, so a road, a crop field or a block of dense trees can permanently cut one colony off from another.
• Prescribed fire, which looks destructive, is one of the main tools used to keep Karner blue habitat open. Managers burn in patches and in rotation so that part of the colony always survives to recolonise the burnt ground.
• Butterflies as small as this are easy to overlook: the whole insect, wings and all, weighs a fraction of a gram and disappears against grey sand the moment it settles.

In summary

The Karner blue, Plebejus melissa samuelis, is a very small endangered butterfly of sandy oak savanna and pine barrens in Wisconsin, Michigan, Minnesota, Indiana, Ohio, New York and New Hampshire. Males are silvery violet-blue above and females grey-brown with orange crescents, while both sexes share a grey underside marked with white-ringed black spots and a band of orange crescents capped in metallic scales. Its green, slug-shaped caterpillar feeds only on wild blue lupine and is tended by ants; the egg is the stage that survives the winter; and there are two broods a year, flying in late spring and again in high summer. Listed as endangered in the United States in 1992, it survives today wherever fire, mowing or grazing keeps its savanna open and its lupine growing.

Karner Blue butterfly pictures

Frequently asked questions about the karner blue butterfly

What does a Karner blue caterpillar look like?

The caterpillar is flattened and slug-shaped rather than cylindrical, plain translucent green with a darker line down the back, a pale stripe along each side and a coat of very short white hairs. The black head stays hidden beneath the body. It reaches about 13 millimetres and grazes the underside of wild lupine leaves, leaving pale translucent windows.

How do you tell male and female Karner blue butterflies apart?

Look at the upper wing surfaces. Males are a bright silvery violet-blue with a narrow black border and a white fringe, while females are grey-brown with blue near the body and a band of orange crescents inside the hindwing margin. From below the two sexes are identical, both showing a grey ground with black spots and orange crescents.

Why is the Karner blue butterfly endangered?

Because its caterpillars eat only wild blue lupine, and that plant has disappeared with its habitat. Sandy oak savanna and pine barrens have been converted to farmland, housing and plantation forest, and the fragments that remain grow shut without fire or grazing. The butterfly was listed as endangered under the US Endangered Species Act in 1992.

Where are Karner blue butterflies found in the United States?

Surviving colonies are found in Wisconsin, Michigan, Minnesota, Indiana, Ohio, New York and New Hampshire, always in sandy savanna or barrens where wild lupine grows. Wisconsin holds the largest populations by a wide margin. The butterfly has been lost from Illinois, Iowa, Maine, Massachusetts, Pennsylvania and Ontario, and some colonies exist only through reintroduction.

What do Karner blue caterpillars eat?

Wild blue lupine, Lupinus perennis, and nothing else. The larvae cannot develop on other lupines or on the garden lupines sold for flower beds. They scrape the soft tissue from the underside of the leaflets, and the plant must be growing in partial shade so that its leaves stay green and soft into midsummer for the second brood.

How long does the Karner blue chrysalis stage last?

About 8 to 11 days in the summer generation. The chrysalis is smooth, rounded, pale green and roughly 8 to 9 millimetres long, and it is formed in the leaf litter, in a crack in the sand or among low stems rather than on the lupine itself. Ants often continue to attend the pupa as they did the caterpillar.

Do ants really protect Karner blue caterpillars?

Yes. The caterpillar has a gland on its back that produces a sugary, protein-rich fluid, and ants of several genera feed on it. While they do, they attack the predatory bugs, spiders and parasitic wasps that attack the larva. Tended caterpillars survive markedly better than untended ones, so the ant community matters as much as the lupine.

How many broods does the Karner blue have each year?

Two. Eggs laid the previous summer hatch in April, and the first adults fly from late May into June. Their offspring produce a second, usually larger flight in late July and August, and the eggs laid by that generation spend seven or eight months in the leaf litter before hatching the following spring.

How long do Karner blue butterflies live?

Adults live only about three to five days, with two weeks being exceptional. Almost everything happens at once: males emerge slightly before females, patrol low over the lupine, and mating takes place within hours of a female's emergence. A female then lays several dozen eggs across her brief life before dying.

Is the Karner blue butterfly dangerous or poisonous?

No. It has no toxins, cannot bite or sting, and its caterpillar has no irritating hairs or spines, so both stages are entirely harmless to people. It is illegal to collect or handle the butterfly in the wild in the United States, however, because it is a federally listed endangered species.