What Do Karner Blue Butterflies Eat?

You may have heard that Karner blue butterflies are picky; but what does that mean exactly? What do Karner blue butterflies eat? Do the adult butterflies have a different diet than their larvae? Are they really as picky as some people suggest? Keep reading! In this article, we’ll explore everything you ever wanted to know about the Karner blue’s diet.

What is the Karner Blue Butterfly?

What is the Karner Blue Butterfly

The Karner blue butterfly is a small butterfly with a wingspan of about an inch. It is mostly blue in color, with an orange band on the underside of its lower wings; the females also have this orange band on the topside of their lower wings.

This tiny butterfly is a subspecies of the Melissa blue butterfly, which looks almost exactly the same but has a much larger range. The Karner blue is endangered and only lives in a few small pockets in a handful of states in the Great Lakes region of the U.S.

The Karner blue larvae emerges from overwintering eggs in April, and the adult butterflies live for only a few days in June. These butterflies mate and lay eggs, which hatch within a week, grow and cocoon before emerging as adult butterflies in August.

This second batch of Karner blues mates and lays eggs, which lay dormant until the following spring.

As mentioned, Karner blues are endangered, and they are threatened by habitat loss as well as weather and climate changes. They are sometimes referred to as a “conservation-dependent” species, so efforts are continually underway to preserve their native habitats and keep them from dying off.

Check out this video to learn more about the Karner blue butterfly:

What Plant Does the Karner Blue Butterfly Larva Eat?

Part of the reason this butterfly is endangered is that its larvae are extremely finicky; they only eat the leaves of one kind of plant, the wild blue lupine.

Wild blue lupine is a member of the pea family. It grows wild in open woodland areas such as oak savannas and pine brush regions, though it tends to become shaded out after a few years as trees and other vegetation take over.

Karner blue caterpillars are unable to travel far, and once their only food source begins to die out in one spot, they will starve to death. Even the adult butterflies, with their ability to fly, tend to stay close to the area of their birth, so they often aren’t capable of exploring new regions and scouting out new food sources for their young.

In areas where wild blue lupine is abundant, Karner blues may thrive for a period of time. The caterpillars are voracious eaters, devouring leaves in between the veins and producing lace-like patterns. 

Caterpillars remain in the larval stage for a few weeks in April and May and again in July. During this time, they will grow significantly and shed their skin several times, all the wild feeding on ever-increasing amounts of the wild blue lupine leaves.

What Plants Do Adult Karner Blue Butterflies Eat?

What Plants Do Adult Karner Blue Butterflies Eat

Adult Karner blues tend to be a little less picky than their larvae; they enjoy eating the nectar from a variety of both wild and domestic flowers. Some of their favorites include:

  • Butterfly weed: Butterfly weed is an orange-blooming species of milkweed and a favorite plant of many types of butterflies, hence the name “butterfly weed.” It isn’t actually a weed, and it is commonly grown as an ornamental plant in home flower gardens.
  • Blazing star: Blazing star is another commonly-cultivated plant that Karner blues love. This plant produces tall flower stalks that bloom from the top down and are typically shades of purple and lavender in color.
  • New Jersey tea: New Jersey tea, also known as mountain snowbell, is a flowering shrub that can grow 3 to 4 feet tall. It is commonly cultivated but may be found growing in the wild as well, and its snowflake-like flower clumps are commonly frequented by any Karner blues in the area.
  • Leafy spurge: Leafy spurge is an invasive plant that was originally native to Eurasia, but it now grows wild throughout the U.S. It is a shrub-like plant that produces bright yellow flowers which Karner blues love.
  • Wild Virginia strawberry: Wild Virginia strawberries are wild ground cover type plants that produce fragrant blossoms in the spring and small red berries in the summer. Their blossoms are a favorite choice of the first batch of Karner blues that fly in June.
  • Goldenrod: Goldenrod is a tall, flowering plant that can be cultivated but that more often grows wild. Its tall, bushy, yellow flower stalks bloom in late summer and fall and are often visited by the second batch of Karner blues that flies in August.
  • Rock cress: Rock cress is an easy-to-grow groundcover that grows both in the wild and in cultivated gardens. These plants spread out like mats and are full of brightly-colored flowers.
  • Raspberry: Wild raspberry plants are common in the Karner blue’s range, and they produce fragrant blossoms in late spring and early summer when the first batch of adult Karner blues are in flight. 


Karner blue butterfly larvae only eat the leaves of the wild blue lupine plant. The adult butterflies are less picky and enjoy eating the nectar of a variety of flowers, including butterfly weed, goldenrod, and leafy spurge.

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