A Heat Wave Makes the Caterpillars Grow

The temperature on the bank in Cable read 94 degrees when I returned from a field trip on June 4. It was only a short walk from the air-conditioned van to the dark, cool lobby of the Museum, but the heat shimmered and blazed beyond its usual Northwoods intensity.

“I just watched through the front doors as a monarch butterfly laid eggs,” were the first words our docent, Carol, spoke from behind the front desk, even before my eyes had adjusted. I turned to look at the small patches of milkweed we’ve let spring up on either side of the Museum’s front walk. No black-and-orange monarch butterfly flitted among them now. No eggs were visible either, but since they are the size of a pin head, I’d need Superman’s vision to spot them from a distance. I did go out the next day—before the temperature rose to another record high—to snap photos of the tiny, translucent domes. One photo even revealed the pale yellow silhouette of a developing larva inside.

Monarch butterfly eggs are tiny and translucent. They are deposited on milkweed leaves, because that’s the only food that the caterpillars can eat. Photo by Emily Stone.

I’ve read that monarch butterfly eggs can take anywhere from 3-6 days to hatch, so I wasn’t quite sure when I should expect to see caterpillars. I figured it would be soon, because warmth speeds up their development process, and we’d had more than enough heat recently.

At temperatures below 52 degrees Fahrenheit, monarch eggs and caterpillars don’t grow or develop at all. On a cool night, their bodies simply pause. Extreme heat isn’t helpful, either. As temps approach 91 degrees, caterpillar growth slows and then stops. They seek shelter on the underside of leaves, or crawl down into the leaf litter to find relief.

If nighttime temperatures are on the cool side, caterpillars once again find refuge underneath milkweed leaves, shielding their body heat from the cold pull of the stars. On days that are not quite warm enough, caterpillars bask on the top of the leaves, orienting their body broadside to the sun, for absorbing maximum solar radiation. Caterpillars who grow up in cooler temperatures may also have wider black stripes, which helps to absorb heat from the sun. Temps between 59 and 84 degrees Fahrenheit seem to be their happiest range, where they can grow the fastest.

A few days after I wrote this article, temperatures plummeted and we hit an overnight low of 40 degrees. These were some cold caterpillars! Photo by Emily Stone

Staying warm hasn’t been a problem this year! [Edit: of course, right after I wrote this article we had a short cold snap!]

Just four days after Carol watched the butterfly lay eggs, I paused on my way into the Museum after my weekend. A little searching revealed a caterpillar or two, and after zooming in on the macro photos, I could even determine that these little critters were in their second instar already.

Monarch caterpillars shed their skin five times between when they emerge from their egg and when they develop into a pupa, each time revealing a larger skin waiting just beneath. Each stage is called an instar. The first instar, when a caterpillar emerges from the egg, is almost translucent, and lacks the distinctive black, white, and yellow stripes we expect. The caterpillars I spotted—just 4 days after eggs were laid—were distinctly striped, and also sported tiny black tentacles on both their head and their rear.

Over the past two weeks, I’ve kept track of these little dudes almost daily. Well, maybe not the exact individuals I first spotted. By my last count there were 30 caterpillars in all stages of development on our small patch of milkweed. I have no idea which ones were my first two friends! With all the bad news about monarch populations in decline, this is a little spot of hope.

Having lots of caterpillars in a single place doesn’t equal a species no longer on the brink of extinction, though. Jan Sharp, a Museum volunteer who also monitors monarchs for the Monarch Joint Venture, noted that in 2012 we had a similar early spring and big first crop of caterpillars. Then, when those caterpillars grew into adult butterflies and began laying their own eggs, danger moved in.

Parasitic wasps lay their eggs on monarch eggs, and the wasp larvae eat it from the inside. A different wasp lays eggs in a newly formed chrysalis, with the same deadly effect. Tachinid flies lay eggs on caterpillars. Lacewing larvae, like tiny crocodiles, devour eggs at lightning speed. And mites, spiders, ants, wasps, and bugs attack the smallest instars.

Caterpillars get safer the bigger they get, and their growth is truly amazing. From freshly hatched to entering their pupa, caterpillars increase their body mass anywhere from 200 to 10,000 times (depending on which source you read) in just two weeks—less if the weather is warm.

I’m not a fan of this season’s heat, but I do love monarchs. Maybe I’ll just watch from my air-conditioned refuge as I cheer “Grow little monarchs, grow!”

Caterpillars eat almost constantly, and can increase in size by 200 to 10,000 times before they become an adult! Photo by Emily Stone.

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is now available to purchase at www.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.

Singing Praise for Caterpillars

Rosy maple moths spend their childhood as caterpillar feeding on maple trees.

Photo by Emily Stone.

“Check out these pretty moths!” The Museum’s new office manager, Hayley Matanowski poked her head in the office door as I was firing up my computer for the day. On the cool concrete patio were two moths with pink-and-white striped wings and fuzzy yellow bodies. As we each scooped one up for relocation, I noticed that even their legs were covered in pink fuzz.

After we released the moths into the shady trees at the edge of the Museum’s outdoor classroom, I uploaded a photo to the SEEK app, which is useful for identifying all types of living things. Rosy Maple Moth popped right up on the screen. When I posted the photos to Facebook, eleven people commented on seeing them recently. Believe it or not, their striking colors are good camouflage among the ripening seed clusters on maple trees, which are often tinged with shades of red and yellow.

My heart soared.

It’s not just that these moths are beautiful. They are an important part of our local food web, and I was happy to hear of these observations. A few weeks ago, when I wrote about whip-poor-wills, I talked to Mike Ward, a professor at the University of Illinois. His words are still ringing in my ears: “Throughout the Midwest there are lots of birds that eat mainly moths and aren’t doing well.”

Moth numbers have gone down in many areas, and that’s bad for more than just the moths themselves. They are on the menu for many species of birds, bats, shrews, frogs, toads, spiders, and other insects.

And that’s just the winged adults.

Moths begin their lives as caterpillars, just like their more visible cousins, the butterflies. Butterflies and moths are both in the order Lepidoptera, which comes from the Greek words for “scale wing,” but butterflies are classified into one subgroup, and moths fall into several. Moth species outnumber butterflies species 10 to 1!

The soft, juicy, caterpillars of butterflies and moths are food for even more critters than their parents. As they munch on plants, caterpillars transform into plump snack packs that are full of fats, proteins, and chemicals called carotenoids, which are the pigments that turn bird feathers yellow. Even much-maligned forest tent caterpillars are food for 60 species of birds and 155 species of insects, plus frogs, mice, bats, reptiles, squirrels, skunks, and bears. Nicknamed army worms for the way they march from tree to tree in a line, they are actually the larval stage of a drab, brown moth.

While groups of forest tent caterpillars are highly visible, there are far more caterpillars hidden away in the bushes than you might expect. Chickadees know how to find them, though! With their super color-sensitive eyes, a pair of chickadees will nab between 6,000 and 9,000 caterpillars each summer, just to feed to their nestlings. And chickadees are just one (adorable) example. Scientists estimate that 95 percent of nesting birds feed their babies insects, with caterpillars being a big part of that group.

This black-capped chickadee has a mouth full of caterpillars ready to feed to a nest full of hungry chicks. Photo by Emily Stone.

So if moths are in decline, that means caterpillars are in decline, and it’s no surprise that many birds (including, but not limited to, whip-poor-wills) are in decline, too. That’s just how the food chain works.

At this point, I bet you’re wondering what you can do to help. Thanks for asking!

There are a few things you can do right in your own yard. The first is to plant native flowers and trees. Native insects are closely tied to native plants. As hungry as baby birds are, caterpillars are even more ravenous. Some caterpillars increase their body mass by 2,000 times between hatching from their egg and entering their pupa for metamorphosis to an adult. That takes a lot of food. And it has to be the right food.

Oaks, poplars, willows and cherry trees are host to a huge number of insects. But many species of caterpillars require a certain type of plant. Monarchs and milkweed are a well-known pair. I recently discovered the larvae of dogwood sawflies, on dogwood shrubs of course. On the other hand, most imported plant species don’t provide good habitat. Many websites have lists of region-specific native plants that support pollinators, birds, and other wildlife.

No matter how many native plants you have in and around your yard, if you also have bright yard lights that confuse the moths, bug zappers (which kill more moths than mosquitoes), and you use pesticides, you won’t be providing good habitat. Treatments that claim to kill only mosquitoes can actually kill caterpillars, bees, and fireflies. That deprives the birds and other critters of their favorite foods and has impacts both up and down the food chain.

With the many environmental issues facing us today, making sure that my yard provides good habitat seems like an easy step in the right direction. I see timely and tangible benefits in the form of lovely native plants, cute caterpillars, pretty pink moths, and well-fed chickadees. Together, the birds and I will sing the praises of moths and their caterpillars!

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is now available to purchase at www.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.

The Season for Northwoods Babies

Summer is the season of babies. Loon chicks ride on Mom’s and Dad’s backs, fox pups play outside their den, and caterpillars munch on milkweed leaves. These critters don’t look or act anything alike, but they do have one thing in common: they are Northwoods babies. And when you stop and think about it, there are many different ways to be born, be young, and grow up in the Northwoods!

Loon chicks get a ride on Mom or Dad. Photo by Emily Stone.

Some babies, like the loon chicks and fox pups, benefit from two devoted parents who share the duties of feeding and protecting their young. Butterflies and moths provide no parental care. They simply lay their eggs on the food plant of their caterpillars—and then fly off! They’ve protected their caterpillars with adaptations like camouflage, bad-tasting chemicals, and the instinct of how best to hide. With many mammals, like deer, bats, porcupines, bobcats, and otters, females care for their young alone.

Lately I’ve been paying even closer attention to the wild babies in my woods, because they are the subject of the Cable Natural History Museum’s 2022 exhibit. Since every living thing is young once (it’s hard to imagine a baby house fly or beetle, but they exist!), there’s a lot to pay attention to! And I’m asking for your help!

This summer, the Museum is hosting a Northwoods Babies Photo Contest. It’s pretty simple: kids and adults of any age are invited to submit their digital photos of baby or young animals, and their hard-working parents. All animals must be Northwoods natives, and may include mammals, birds, reptiles, amphibians, fish, and insects. The photos don’t even have to be from 2021. If you got a great photo last summer, you could enter that, too!

The submission portal isn’t quite set up yet, but you can start taking photos now, and then visit our website, www.cablemuseum.org, for the details later. The deadline for entering the contest will be September 1, 2021. After that, we’ll award prizes for first, second, and third place winners in both the under-18 and the over-18 categories, and also let the public vote in a People’s Choice award! Plus, every photographer will be entered into a drawing for more fun prizes. Big thanks to James Netz Photography in Hayward for sponsoring the contest!

Now, I said before that the photo contest is pretty simple, but taking good photos of wildlife is anything but simple. For advice, I reached out to Keith Crowley. Keith has been making photos for more than 35 years, and a few years ago he nabbed some amazing shots of baby gray foxes at the Cable Community Farm.

Two gray fox pups play at the Cable Community Farm. Photo by Keith Crowley, https://www.lodgetrail.com/.

“Your primary asset is patience,” he told me, “Patience to the extreme.” For 26 days, Keith parked his vehicle a respectful distance from the fox den—which was located by the back steps of the Farmhouse—and sat for countless hours waiting for the foxes to do something interesting. He captured shots of the three cubs playing together, of the parents bringing ground squirrels for dinner, and, finally, of the cubs climbing a nearby crabapple tree. Gray foxes are pretty unique in their tree-climbing habits, so photographing that behavior was his ultimate goal.

All the while, he made sure to be respectful and ethical. “The critical thing is that you don’t disrupt the family interaction,” he told me. And that’s something for all photographers to remember. “I would prefer that the animal doesn’t even know I’m there,” said Keith. “But the main goal is not to affect their behavior. When they start noticing you, you’ve crossed the line. Then it’s best to back off, or even leave the area.”

This is especially important to remember with birds, who are almost all protected by the International Migratory Bird Treaty. It’s illegal to disturb a nest, or even possess a broken egg or lost feather unless you have the right permits. It’s also essential that you don’t get too close to a nest in the days before the chicks fledge. If you scare them out before they’re ready, their chance of survival goes way down. If you think a baby animal needs help, there are plenty of resources online to help you figure out what to do (or not do!).

Recently, Keith spotted a young fawn nursing outside his kitchen window. The photos would have been super cute, but he had no way to get his camera into position without disturbing the pair, and then the fawn would have missed a meal. That’s not ok, so Keith just watched quietly.

One way to get close to animals without disturbing them is to camouflage yourself. That could take the form of a blind, a vehicle, or camouflaged clothing like a ghillie suit. “Growing up hunting,” Keith told me, “you learn that the best camouflage is being still.”

Of course, some animals are more comfortable around humans than others, and if there’s a family in your yard, you can often sit quietly and let the critters get used to you. One of Keith’s favorite interactions was finding a baby porcupine who sat calmly at eye level in a tree at the top of the driveway for a whole week! Insect babies, like caterpillars and dragonfly nymphs, will often be cooperative models.

One of the best parts about going in search of a great photo is that it challenges you to observe nature more closely. You never know what you’ll find! So, take your camera outside, and (respectfully) enjoy the season of babies!

A tiny monarch caterpillar crawls along the midrib of a milkweed leaf. Babies are often small! Don't forget to look closely! Photo by Emily Stone. 

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is now available to purchase at www.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.

Whip-Poor-Will

The full moon was last week, and do you know what that means? Well, full moons signify many things to many people, but to whip-poor-wills, it means they’d better get busy if they want to give their chicks the best chance at survival.

Whip-poor-wills time their egg-laying with the phases of the moon.

I’m typically skeptical of such fanciful claims, but this one has been supported by the research, and by common sense. The brown-speckled birds become active only at dusk and dawn, and use the last and first light of day to spot insects silhouetted against the sky. Then they flutter up from their perch to scoop moths out of midair. A full moon means more light to see by, and more hours with visibility for catching bugs, which they regurgitate for their young. So, by timing mating and the laying of their two eggs just right, whip-poor-wills schedule their chicks to hatch 10 days before the full moon. Growing chicks will reach their hungriest stage just when the moonlight provides the maximum number of hours for foraging.

So if chicks need to hatch 10 days before the next full moon on June 24, and they need 19-21 days of incubation…let me count backward on my lunar calendar…that means that their parents likely mated just a few days before this recent full moon. The extra light likely helps the female admire the male as he performs his courtship display. It’s no wonder that Museum Director Deb Nelson came into my office recently and said “You should write about whip-poor-wills this week!”

“Have you been hearing them again?” I asked, already knowing the answer, since every spring since I’ve arrived at the Museum, Deb has told me how much she loves listening to the whip-poor-wills call in the woods behind her home north of Cable, Wisconsin. While their emphatic and incessant call may not be instantly recognizable, once someone has told you that they are saying their own name, it is certainly unforgettable.

Whip-poor-wills are known to call more frequently when the moon is at least 50% illuminated. This is useful information for the people who do breeding bird surveys and attempt to count whip-poor-wills on the landscape. It makes behavioral sense, too, since a nightlight means more time to be active. Plus, a male whip-poor-will needs to throw all his energy into attracting a mate and defending his territory—two activities that require him to sing loudly—in the nights leading up to the actual act of mating. Which, by my calculation above, occurs just before the full moon.

After mating, the female lays two well-camouflaged eggs directly on dry ground in a shady patch of leaf litter. Building a nest would just provide a bigger target for predators to look for. Once the chicks are about 8 days old, they hang out exclusively with Dad, while Mom often starts a second nest.

Eastern whip-poor-wills are extremely well-camouflaged and rarely seen. It’s likely you’ve heard one shouting its name, although maybe not recently as their numbers are declining. Photo by Mirko Schoenitz, posted to iNaturalist and used under Creative Commons.

“Why do they sing only at night?” was the next question that Deb posed to me. It’s a good question, and one that scientists have many answers to, none of them definitive. Maybe the birds prefer the quiet that comes with darkness. During the day, whip-poor-wills would have to compete with dozens of other bird species, plus wind noise and air turbulence.

Or maybe, since the gray-and-brown mottled whip-poor-wills spend all day hunkered down on a low limb or the ground—virtually invisible—calling during the day would alert predators to their presence and ruin their perfect camouflage. Nighttime has fewer predators, and more things to accomplish. Whip-poor-wills do their courting at night, so it’s important for the male to conduct his vociferous flirting and territorial defense when the ladies (and competing males) are also out looking for love.

Every year, when Deb tells me about hearing her whip-poor-wills, my response is “Do you know how lucky you are?” Just like the golden-winged warblers I wrote about last week, whip-poor-wills are an example of a common bird that is in decline. Over the past half-century, their numbers have dropped by 75%. While they are still common in some places—like Deb’s yard and the Moquah Barrens on the Bayfield Peninsula—they have disappeared from other places. Nights are quieter now in my neighborhood between Cable and Clam Lake, and even in my parents’ patchwork of prairie and woods in northeast Iowa where whip-poor-wills kept me awake as a kid.

So what is causing their decline?

Mike Ward, a professor at the University of Illinois who has been geotagging Whips in the Moquah Barrens, emphasized the relationship between the whip-poor-will population and moths. He knows it’s a strong connection, because in his words, “the birds give us a fecal sample when we tag them,” and that sample is full of moths. He also told me that “throughout the Midwest there are lots of birds that eat mainly moths and aren’t doing well. When I drive around the Barrens at night, my windshield gets covered with moths, but that doesn’t happen in other areas where the whip-poor-wills aren’t doing well.”

The connection extends to other birds (like golden-winged warblers) who eat insects, too. It’s inevitable that humans’ war on insect “pests” has impacts far up the food chain. If we get rid of all the caterpillars chopping away on plants, they can’t metamorphose into moths. And without moths, whip-poor-wills will have trouble feeding their young.

You can make a difference in your own backyard by preserving and restoring habitat, planting native species, spraying fewer chemicals, and leaving messy areas. Together, we can help whip-poor-wills rise and grow like the waxing moon.

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is now available to purchase at www.cablemuseum.org/books. Or order it from our friends at redberybooks.com to receive free shipping!

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.