During spring in the Rocky Mountains it is common to see a Mourning Cloak butterfly.  These butterflies in the spring appear to be ragged and tattered.

Many animals choose different strategies to survive winter, such as migrating, hibernating, or adapting.  When we think of the animals that spend the winter in the Rocky Mountains hibernating we most likely think of bears.  We have all learned about bears ‘hibernating’ at some point in our lives.  However, there is another tiny animal that also overwinter in the Rockies that you may not be aware of.

Why Are Mourning Cloak Butterfly Seen In Spring?

These butterflies are commonly seen in the spring because they spend the entire winter in the Rocky Mountains in their adult form.  Many other butterflies choose a different strategy to survive winter, such as migrating.

Instead of simply leaving, these butterflies find a nice hole in a tree, or spot under bark to protect them from the harsh winter.  They spend all winter hidden in their spot, hopefully safe from the weather and predators.  This explains why the Mourning Cloak butterflies that you see in the spring often look ragged and tattered.  It is because they just survived all winter as an adult!

How Do Do They Survive Winter?

They enter a state of dormancy, called diapause.  This is similar to hibernation in which they simply are very inactive and resting.  Since insects are cold blooded animals their body temperature drops to the outside temperature, which can be below freezing during winter.

Mourning Cloak butterflies and other insects are able to survive winter and not freeze by reducing the amount of water in their bodies.  They replace the water with glycerol, which is similar to the anti-freeze people put in our cars.

About Mourning Cloak Butterfly Lifecycle

The adults emerge in the spring and sit in sunny places to warm up. Then the adults will mate and lay eggs.  The caterpillars are born and after a short time pupate into adult butterflies, emerging sometime in June/July.

Then it is not uncommon for adults to aestivate, which is a form of hibernation that animals enter during a hot, dry time of year.  Finally, the adults will awaken in the fall to eat and prepare for winter again.