How Many Eggs Does A Karner Blue Butterfly Lay?

Different types of butterflies lay different numbers of eggs; the number can depend on the butterfly’s size and lifespan, among other environmental factors. Today, you’re wondering, how many eggs does a Karner blue butterfly lay? What time of year does this butterfly lay its eggs? What is the Karner blue’s life cycle? Keep reading to find out answers to all of these questions.

How Many Eggs Does a Karner Blue Lay?

How Many Eggs Does a Karner Blue Lay

Karner blues are tiny butterflies, with small bodies and wingspans no more than an inch in diameter. 

You’ve probably heard that they’re endangered, and you may think that part of the reason for this is that they are too small to lay enough eggs to reproduce at a fast enough rate to keep their own species going, but this isn’t entirely true.

Karner blue butterflies do lay fewer eggs than some types of butterflies. A female Karner blue may lay as many as 80 eggs in her lifetime; by comparison, the much larger tiger swallowtail may lay up to 250 eggs.

That said, 80 eggs from such a small butterfly is quite impressive. It’s thought that about 40 to 50 percent of eggs laid survive to adulthood; so if each mating pair produces 30 to 40 adult butterflies which can then mate and reproduce themselves, the problem of endangerment isn’t necessarily the number of eggs laid.

Karner blues lay their eggs on or near wild blue lupine plants, as the leaves of these plants are the only thing their larvae will eat. Yearly numbers of Karner blues depend on the success of overwintering eggs, which may be destroyed if large areas of wild blue lupine are torn out or if periods of unseasonably warm weather cause them to hatch too soon.

What’s more, habitat loss can lead to starvation for entire populations of Karner blue caterpillars in localized areas. For example, too many eggs may be laid in areas where the wild blue lupine is dying out due to succession.

In some regions, efforts have been made to relocate Karner blue eggs from areas where wild blue lupine is dying or about to be torn out to areas where it is thriving. This is, of course, because the survival and restoration of this endangered butterfly begins with saving its eggs.

Check out this video of a Karner blue laying eggs. You’ll notice it is laying eggs on a pitch pine rather than wild blue lupine; undoubtedly the host plant is nearby.

What Time of Year Do Karner Blues Lay Eggs?

Karner blues have two generations each year. The first generation hatches from overwintering eggs in April or May.

This first generation reaches adulthood in June and lays eggs. This second batch hatches, reaches adulthood by August, and lays eggs that will overwinter and begin the cycle next spring.

So, Karner blue eggs are laid in June and August.

What is a Karner Blue Butterfly’s Life Cycle?

The Karner blue’s life cycle is divided into four stages: egg, caterpillar, chrysalis, and butterfly.

Egg stage

As noted above, each female lays up to 80 eggs in June and again in August of each year. These eggs are laid in groups on the stems and leaves of wild blue lupine plants, and they are just 1 millimeter in diameter.

The eggs laid in June hatch after about a week; those laid in August remain dormant for several months before hatching the following April or May.

Caterpillar stage

Karner blue caterpillars are very tiny when they first hatch. They spend the next few weeks eating wild blue lupine leaves, growing rapidly and shedding their skin from time to time.

These caterpillars are light green in color, somewhat stubby and flat in shape. They have a symbiotic relationship with ants; the ants perform a grooming type behavior with the caterpillars, the caterpillars secrete a sweet liquid which the ants eat and which protects the caterpillars from parasites.

After a few weeks, the caterpillars are ready to enter the next stage of their life.

Chrysalis stage

When they are ready to pupate, or morph into a chrysalis, the caterpillars choose a sheltered location on the underside of a leaf or in nearby leaf litter. They shed their skin one last time, exposing the small, green chrysalis.

The butterfly remains in this stage for about 8 to 11 days, during which time the caterpillar cells morph into the mature cells of the adult butterfly. When the butterfly is ready to emerge, the chrysalis darkens and may begin to show some of the blue-gray coloring and spotted patterns of the butterfly inside.

Butterfly stage

The thin skin of the chrysalis splits open and the butterfly crawls out. For the next 45 minutes or so, it must hang from a leaf or branch, allowing its wings to dry and straighten.

Adult Karner blue butterflies may only live for a few days, though some females have been known to live for up to two weeks. They spend their short lives nectaring on flowers, resting during the heat of the day, mating, and laying eggs, all in areas within 600 yards of their birth. 


Karner blue butterfly females tend to live longer than males; some will live up to two weeks, and during this short lifespan, each female will lay up to 80 eggs. Karner blues come in two batches per year: the first emerges from overwintering eggs and lays eggs in early to mid-summer; the second batch emerges from these eggs and lays the eggs that will lay dormant through the winter in late summer. 

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