Or, How Does a Red-spotted Purple
Spend the Winter?
Understanding the life cycle and natural history of resident butterflies in our wildlife gardens plays a more important role than you may think when it comes to decisions regarding maintenance and other garden tasks.
Many of the moths and butterflies we’ve attracted to our gardens spend the winter in the garden as an egg, a partially grown caterpillar, or a chrysalis. Many spiders and preying mantises lay egg masses that over winter too; the adults die as late fall arrives.
Red-spotted Purples are quite common in our garden from mid-June through late September. We have lots of Black Cherry trees (Prunus serotina) and have also planted Beach Plum bushes (Prunus maritima). Both are used as caterpillar host plants by this stunning butterfly.
On September 23, 2012, I watched one of the very last Red-spotted Purples in the garden. It danced around the Beach Plums and I thought it must be laying eggs. I looked closely at leaf after leaf, zeroing in on the very tip where Red-spotted Purples carefully lay their jewel-like egg, but could find none.
Going to Bed for the Winter
As I scrutinized the leaves, though, I suddenly spotted a treasure – a teeny-tiny caterpillar (@ 1/4 inch long) perched out near the end of a twisty, dead-looking bit at the end of a leaf. I stepped back from the Beach Plum, looked at the bush as a whole, and noticed other similar leaves with dead-looking extensions. Each one had a teeny-tiny Red-spotted Purple caterpillar on it, four all told.
I ran for the camera, knowing just what I’d found: Red-spotted Purple caterpillars preparing their winter hibernaculum, the place where they will safely winter as a partially grown caterpillar.
Every day thereafter I spent time searching for the caterpillars, hoping they’d survive. It was the peak of autumn migration and our little woodlot attracted flock after flock of hungry migrant songbirds. Each day I feared that my caterpillars would be gone, discovered and feasted upon by hungry birds.
Five days later, September 28, I found only two of the four caterpillars. Each of them had completed their hibernaculum and was hiding down inside. They’re still there, hopefully safe for the winter.
Come winter, Black Cherries and Beach Plums lose their leaves. Red-spotted Purple caterpillars silk the hibernaculum leaf closed and to the branch. When all the leaves fall these hibernaculums will be the only remaining leaves on the tree (or shrub) through winter, making hibernaculums a bit easier to spot.
Over the winter these tiny caterpillars could still succumb to a hungry bird inspecting every inch of every branch for a morsel. Overwintering caterpillars are just such a morsel. Heavy snowfall could snap off the twig supporting the hibernaculum. An ice storm coupled with strong winds could do the same.
In the Spring
If all goes well, by spring the overwintering, partially-grown caterpillar will emerge from the safety of its hibernaculum to feed as Beach Plums and Black Cherries leaf out.
Once full grown, the caterpillar will go into the next life stage, an amazingly camouflaged chrysalis (see below). About 12 to 14 days later the first generation of flying adult Red-spotted Purples will emerge from the chrysalis in mid-June in southern New Jersey. I can hardly wait.
Other Parts of the Red-spotted Purple’s
I’ll be Looking Closely for More Hibernaculums This Winter
With the hibernaculum search image now intact, I’ll be looking more closely at each and every leaf bit still attached to Beach Plums and Black Cherries. Too, I’ll be keeping my fingers crossed that the tiny caterpillars will survive the winter and its many hazzards: hungry birds, heavy snow, ice storms and strong wind, as well as fussy, too-tidy gardeners.
Pat Sutton, of Cape May NJ, is an author and naturalist who has taught gardening for wildlife workshops and tours, for over 30 years, and is available to speak to your group or organization.
© 2012, Pat Sutton. All rights reserved. This article is the property of Native Plants and Wildlife Gardens. We have received many requests to reprint our work. Our policy is that you are free to use a short excerpt which must give proper credit to the author, and must include a link back to the original post on our site. Please use the contact form above if you have any questions.