By Rene Stroud, Pottawattamie County Conservation Naturalist
In the summer Iowa is home to about one hundred breeding species of butterflies providing that season with a flurry of color and beauty. You may be wondering where do they all go in the winter? The monarch butterfly gets a lot of deserving attention for its amazing journey to Mexico, but what about the rest of them? How do such small,l fragile creatures withstand Iowa’s harsh, blustery winters?
The key is overwintering in a state of suspended animation. They may overwinter as an egg, as a larva, pupa, or even as adults. There are two main ways that they deal with these temperatures without perishing. One way, at least for adults and larvae, is to accumulate high concentrations of sugar in their blood. The sugar acts as like antifreeze and keeps their blood from becoming solid. Solutions with a high concentration of sugars freeze at much lower temperatures; try placing a small amount of pure maple syrup in your freezer to test this theory. Does the syrup change consistency? The other way involves forcing the water in their cells outside of the insects’ bodies. This allows the water to freeze externally without injuring the butterflies’ cells.
My interest in overwinter butterflies all started one chilly January day, when I noticed a small brown shape hanging on the outside of my house above the herb garden.
I didn’t think anything of it until upon closer inspection I realized it was a black swallowtail chrysalis. I was baffled. I had seen them in the summer as caterpillars munching on my dill. I did some research and found that the vast majority of swallowtails overwinter as a pupa. This discovery led me to further research and I discovered a number of commonly seen butterfly species with fascinating strategies to survive the chill of Iowa winter weather.
The mourning cloak is a unique butterfly; they are commonly seen flying around before the snow completely melts in the spring. I have seen tattered morning cloaks visiting snow trillium on warm early spring days as early as the end of March. They overwinter as an adult in protected crevices such as loose bark, log piles, and in the cracks of buildings. When temperatures reach 60˚F they can reanimate to find food, like tree sap and scat. This butterfly can live up to 10 months old, an incredible lifespan for an insect. It is thought that they sequester themselves again in the summer and re-emerge in early fall.
The red admirals are an enigma to the scientific community with conflicting overwintering behaviors reported in a number of common guidebooks. Some say they do not overwinter in Iowa (Opler and Malikul 1998. While others imply that they overwinter as adults in crevices and/or die off during the winter (Stokes and Williams 1991). Yet, according to Butterflies of Iowa, the first individuals of spring are unmarred and newly emerged (Schlicht, Downey and Nekola 2007). This would indicate that they did not overwinter as an adult as species that overwinter as adults are well worn from their fall activities and show their age in wing damage. In the spring, there is a recorded pattern of some red admirals that migrate into our area from the south.
#1 – Red admiral larva, By Harald Süpfle (Own work) [CC BY-SA 2.5 (http://creativecommons.org/licenses/by-sa/2.5)], via Wikimedia Commons from Wikimedia Commons
#2 – Red admiral chrysalis, By Emmanuel Boutet (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html), CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/) or CC BY-SA 2.5-2.0-1.0 (http://creativecommons.org/licenses/by-sa/2.5-2.0-1.0)], via Wikimedia Commons from Wikimedia Commons
The viceroy may look like a monarch but unlike their more well-known doppelganger, they do not migrate. Viceroys overwinter in larval form. When the temperature drops the small caterpillars eat away the tips of a leaf on either side of the midvein. Then they curl the base of the leaf into a little tube and secure it with silk. The whole leaf is reinforced and secured to the tree with silk and this tiny winter home is called a hibernaculum. Hibernacula can be found on host trees like willows, aspens, cottonwoods, and fruit trees. During the depth of the winter these are sometimes the only leaves left on the tree.
Winter is a great time to grab a magnifying glass and head out to any of your local county parks on a butterfly expedition. Check area trees for hibernacula that may contain viceroys, keep your eyes peeled and look for hollows and crevices that may house mourning cloaks, and always please be sure that you don’t disturb these amazing insects as you seek them out. Take a few minutes to learn more about these beautiful and remarkably resilient creatures.
Winter Butterfly Searching Tips:
Look for overwintering butterflies in the same areas they inhabited during the warmer months.
Keep a sharp eye out for protected areas that provide a waterproof cover like crevices in trees, under bark, or in any little nook or cranny.
Inspect the few remaining leaves on trees and in the leaf litter for silk.
Be kind and take only pictures and try to leave everything as you found it.