Why Is The Karner Blue Butterfly Endangered?

If you’ve never heard of the Karner blue butterfly, you’re not alone. This small blue butterfly only lives in isolated areas of the United States, and its numbers are dwindling. In fact, it has been on the United States’ Endangered Species list for two decades. So, why is the Karner blue butterfly endangered? How many of them are left in the wild? Is anyone or anything impacted by their endangerment? Keep reading as we answer these questions and more.

Why is the Karner Blue Butterfly Endangered?

Karner Blue Butterfly

Karner blue butterflies are small blue butterflies with orange bands on their lower wings. These butterflies are found in scattered spots throughout parts of the Great Lakes and New England regions of the United States as well as parts of Canada.

These butterflies have experienced a great decline in numbers over the past few decades. They have been listed as a federally endangered species since 1992. 

There are several factors that have contributed to this butterfly’s endangerment. These factors include:

Habitat loss

Karner blue butterfly larvae only feed on one type of plant–wild blue lupine. This low-growing flowering plant is found primarily in oak savannas and other wooded areas.

The problem is, in its natural habitat, wild blue lupine eventually dies off as the trees grow larger, blocking out the sunlight and sapping the soil of nutrients. So, as its food source dies off, the caterpillars starve.

What’s more, Karner blues rarely travel more than 600 feet from the place of their birth, even as adult butterflies. So, once the wild blue lupine dies off in their area, the butterflies begin to die off with it rather than travel to a new area in search of more.

Climate change

Climate change also affects the Karner blue’s numbers because these butterflies need a consistent snowpack throughout the winter months to keep their eggs dormant until the proper season. Warmer winters can lead to overwintering eggs hatching out too early, before the wild blue lupine has emerged in the spring. 

Weather changes

Extreme weather can affect all types of butterflies and insects, but it may have a greater impact on Karner blues because their populations are more scattered than other species. If severe weather or extended periods of drought strike one of these areas, an entire population of the butterflies and their larvae can be wiped out in a relatively short period of time.

How Many Karner Blue Butterflies are Left?

How Many Karner Blue Butterflies are Left

As mentioned, the existing populations of Karner blues are scattered and somewhat separated from each other. While they used to exist in a band across twelve Great Lakes states and neighboring regions of Canada, they have disappeared from seven of those states.

Their numbers have fallen so dramatically that, in some states, they are protected locally as well as federally.

In many of their scattered locations, there are fewer than 1,000 butterflies at a given time. Though they used to be found in Ontario, Iowa, Illinois, Massachusetts, Ohio, and and Pennsylvania, they have been extirpated from these areas.

What is the Population of the Karner Blue Butterfly Today?

It’s impossible to say exactly how many of these butterflies are left in the wild because their numbers fluctuate from season to season. The individual butterflies have extremely short lifespans, as the adults rarely live for more than a week after emerging from their chrysalis; therefore, it’s nearly impossible to track their exact numbers. 

That said, it’s possible to get an idea of how their numbers have declined by looking at the data provided by specific regions. 

In Ontario, for example, there were about 1,000 Karner blues in 1984. In the following years, drought and unseasonable cold periods eliminated this population entirely, and no Karner blues have been seen in the province in over 30 years.

In the state of New Hampshire, there were as many as 5,000 Karner blues in the 1980s. Less than 15 years later, fewer than 50 were counted.

Though overall numbers have likely improved since that time due to awareness and conservation efforts, Karner blues are still considered endangered and will likely remain so as long as habitat loss, climate change, and bouts of bad weather exist to threaten the individual populations.

Who is Impacted by the Endangerment of the Karner Blue Butterfly?

Every creature within an ecosystem has an impact on all the others, however small that impact may be. 

The Karner blue butterfly’s caterpillar has a symbiotic relationship with ants. The ants feed on a secretion produced by the caterpillars and, in return, provide some level of protection against predators that would otherwise eat the caterpillars.

These ants may be impacted by the Karner blue’s endangerment because, if there are no larvae producing the secretions for the ants, they will lose one of their food sources.

Of course, ants are fairly adaptable and, if they are no longer receiving one food source, they will simply move onto another one. Still, it’s hard to say exactly how much local ant populations would be affected if Karner blues were to go extinct altogether.


Karner blue butterflies began declining significantly in the 1970s and 80s and, though efforts have been made to restore their numbers, they remain a federally endangered species. They are endangered for several reasons, but the most significant factor is the loss of habitat–the plant their larvae feed on, wild blue lupine, tends to die out after a few years in an area, and the butterflies seem unable to move to other areas where it crops up. 

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