A certain sign of spring

As we move into April, the warmer days may finally be here to stay. With the promise of lasting spring, we will likely see a number of animals emerge from their winter daze. Many adult butterflies have spent the winter tucked away in tree cavities, under bark, or in unheated buildings frozen in a sort of cryo-preservation. So they too will begin to rise from their dormancy. One that is commonly first seen in Minnesota is the mourning cloak butterfly. This species uses a number of adaptations for its early emergence, and may have already started to come out of hibernation.

The mourning cloak butterfly, so named for its resemblance to a traditional cloak worn when one was “in mourning,” has a unique appearance that distinguishes it from all other butterflies. Its wings are mostly dark, with a white to yellow outer margin and blue spots along the edge. They inhabit a wide range throughout the world, spanning North and South America and across Europe and Asia. They prefer to live in areas along river banks, but can be found anywhere their host plants grow, including forests, parks and suburbs. Adult butterflies feed on the sap of oak or maple trees, but will occasionally opt for rotting fruit or flower nectar. Mourning cloak butterflies will emerge from hibernation in March or April. They come out of dormancy around the same time tree sap starts to flow, which becomes their main source of food. After the long winter, mourning cloak butterflies will also begin to search for mates. Males will defend territories and fly around to find a female. The female lays fertilized eggs on the branches of a single small tree or shrub. After mating and egg laying these adults soon die having spent as much as 10 months as adults, a long life for a butterfly.

Mourning cloak caterpillars are black with white specks, two rows of red spots, and long spines along their back. They spend this stage of their life cycle grouped together on the leaves of their host plants. These include willows, elms, poplars and hackberry species. If the caterpillars exhaust the leaves of one plant, they will march single file until they find another food source. When threatened by a predator, the caterpillars will shake in unison to ward it off. After the caterpillars reach full growth, around June or July, they will head off in search of a site to pupate. The mourning cloak will spend up to 15 days in its chrysalis, or shorter if the weather is warmer.

Once they emerge from the pupa stage as adults they must go in search of food in preparation for winter. Butterflies need to have warm wings in order to fly, so they will often lie in the sun and bask. The dark color of the mourning cloak’s wings help to absorb sunlight in order to warm up quickly. However, if mid to late summer conditions are too hot and dry they enter a period of aestivation. Aestivation is the summer equivalent to hibernation, when animals escape the oppressive heat by lying dormant in cool shaded places. When temperatures have cooled in early fall, they will begin feeding once again to store energy for the long winter ahead. With its 10 month lifespan, the mourning cloak is the longest-lived butterfly.

Mourning cloaks and other butterflies have a natural winter mechanism that allows them to stay alive through the long season. Their cells generate glycerol, a natural antifreeze that prevents their bodies from forming ice crystals. With this mechanism, butterflies can tuck themselves away inside the holes of trees or in the cracks of buildings. They will remain there until temperatures are warm enough for them to emerge.

Curious what other animals to expect this month? Visit North Mississippi Regional Park to spot some yourself! Traverse the paved trails that wind along the Mississippi River. Visit the Kroening Interpretive Center for our resources on the outdoors. Come see the art installation Putting Down Roots, featuring fiber art depictions of prairie wildflowers, before it’s gone May 1. Identify a variety of birds up close at our bird feeder station. Spend a day learning at our Naturalist Nature Table on Saturdays from 11 a.m.-3 p.m., or enjoy quality time with your family at our Family Fundays every Sunday from 12:30-3:30 p.m. Register for our summer camps to continue the fun all season!

April Public Programs: April 1 – Early Birding: Search for birds while on a naturalist-guided hike. 9-10:30 a.m., free for all ages. April 15 – Fairy Gardens: Create a delightful garden to take home for the fairies! 1-2:30 p.m., $5, all ages. April 22 – Earth Day Celebration: Nature exploration activities, cleanup and springtime art. 11 a.m.-3 p.m., free for all ages. April 30 – May Day Baskets: Craft a lovely basket filled with your own handmade flowers and treats. 1:30-3 p.m., free for all ages.

Kids Spring Break Camp – April 3-7 Nature Art and Adventures: Let your outdoor adventures inspire nature based works of art. M-F, 8 a.m.-4 p.m., Ages 6-12. Registration fee $150.

For info or to register for programs at North Mississippi visit minneapolisparks.org and like us on Facebook to stay in the loop about what’s happening in our park!

Written by Lynn Hu, MPRB Naturalist at North Mississippi Regional Park