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The caterpillars of the Harris’s checkerspot butterfly feed in groups, use web tents for protection, and only eat the leaves of flat-topped white aster. Throughout their life cycle, this species will use three layers of habitat. Photo by Emily Stone.
Every afternoon the museum’s pollinator garden draws me outside with the magnetic pull of its beauty, and the possibility of discovering something new.
I’m rarely disappointed.
This week, while following the darting flights of a calico pennant dragonfly, a weird pattern caught my eye. On a knee-high plant, a few narrow, pointed leaves had been laid up against the stem and wrapped in webbing. They looked a little worse for the wear.
If the holes in milkweed leaves can tell you where to find monarch caterpillars, then this web probably held something interesting, too.
I didn’t have to get much closer to see a swarm of dozens of tiny caterpillars feeding on the leaves, with some staying protected inside the web tents. Despite their tiny size, clusters of bristles erupting from nodes all around the caterpillars’ body segments made them seem rather stand-offish. In translucent shades of cream and brown, they weren’t much to look at.
Still, after a few photos and a visit to iNaturalist.org, I had a name for them: Harris’s checkerspot. These were the larvae of a pretty orange butterfly with black markings – smaller, and softer-looking than a monarch. In order to be sure, I also had to identify the plant they were eating.
My PlantNet app, and the Minnesota Wildflowers website, both helped to confirm: flat-topped white aster, Doellingeria umbellata. This is the only food in the entire world that this species of caterpillar can eat.
Of course, that’s not terribly unusual. Monarch butterfly caterpillars can only eat milkweed. Rosy maple moth larvae focus on maple trees. Aphrodite fritillary caterpillars munch only on violet leaves. Oil bee larvae can only develop on a diet of floral oil and pollen from loosestrife flowers.
Adult Harris’ checkerspots are not nearly so picky. They sip nectar from a bounty of blossoms. In contrast, hairy-banded mining bees (who were featured in our Bee Amazed exhibit a few years ago) specialize in foraging on goldenrod flowers. They won’t even emerge from the ground nests where they overwintered until their favorite flowers bloom in August.
With all of these picky eaters and close relationships in the world of pollinators, the diversity of native flowers in our pollinator garden is what really makes the difference. Each insect can find something it needs as both a larva and adult, and each flower can attract someone to move its pollen. Plus, with so many different flowers, we have something blooming all the way from early spring into late fall.
This week, something else caught my eye. Heather Holm, author of Pollinators of Native Plants, and an expert adviser on our bee and pollinator exhibits, posted two new graphics to Facebook. One of the beautifully drawn, four-paneled handouts talks about keystone species, which means plants like oak trees that are food for at least 940 species of caterpillars.
The other graphic introduces the concept of “soft landings.” Heather’s website explains that, “Soft landings are diverse native plantings under keystone trees (or any other regionally appropriate native tree). These plantings provide critical shelter and habitat for one or more life cycle stages of moths, butterflies, and beneficial insects.”
She’s advocating for people to use the tree’s own leaves to build up soil and duff around its trunk, and add shade-tolerant native plants to create a cradle for those caterpillars to fall into when it’s time for them to pupate or overwinter.
“It’s a great place for a beginner to start making a difference in their own yard,” Heather told me.
If you’ve been to our Mysteries of the Night exhibit, you know that this habitat could benefit fireflies, too!
I’ve been learning about and teaching about leaf litter and “messy” yards as good habitat for a while, but this was the first time I really saw the life of butterflies and other insects in layers.
First there’s the canopy of flowers that provide nectar for the adults, and pollen for baby bees.
Then there’s the understory of leaves – which might actually be overhead – that the caterpillars need to eat. And finally, the ground layer of loose soil, dead leaves, and rotting logs is essential for these insects to complete their life cycles and survive the winter.
“Plant diversity will yield butterfly and moth diversity,” Heather reminded me. And that includes the dead and rotting plant parts, too! For example, the Harris’s checkerspot caterpillars that first caught my eye this week overwinter as large caterpillars in the duff under their favorite aster – ready to resume feeding again in the spring, before pupating and emerging as a butterfly in late June.
I’m going to make sure that our “messy” pollinator garden continues to attract a diversity of life, and provide all the layers of habitat they need to live.
Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is now available to purchase at cablemuseum.org/books and at your local independent bookstore, too. For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. The Museum is now open with our exciting Mysteries of the Night exhibit. Connect with us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.