A Trend of Predaceous Diving Beetles

As a naturalist, I get the strangest emails. I try not to check them at home, but when my phone buzzed and the subject said “June bug on steroids?” it was worth interrupting my evening chores. “The past couple nights I’ve heard something hit our window at night when we have lights on and each time I’ve thought ‘that sounded like a June bug… but BIGGER.’” wrote a Museum member.

I opened the video, and sure enough, there was a black, oval-shaped beetle about an inch and a half long walking along the boards of a deck. The message continued, “I’ve never seen a beetle so big here in the Northwoods. Hopefully it’s not a sign that all of the bugs will be mega sized this year after such a weird winter.” Chuckling, I wrote her back, “Looks like a predaceous diving beetle! That’s their normal size!” The next day, I was scrolling through a Facebook group of regional nature observations, when a video of a diving beetle squirming in a bucket popped up with the caption “Biggest June bug ever!!!” Since June bugs are actually beetles, too, I applauded them for getting close.

Predaceous diving beetles regularly fly between bodies of water, and these 1.5 inch-long insects have been observed around homes recently. June bugs look similar, but are only an inch long and don’t have the large, paddle-like back legs of their aquatic cousins.

Have you heard the saying, “two is a coincidence, three’s a trend”? Arriving home from work, a black spot on the shrinking pile of snow near my front door caught my eye. Yep, there was a predaceous diving beetle! Despite being chilled, he was very wiggly once I flipped him over. There was a wide patch on his front leg, which is a character of the males only. I snapped some photos and then scooped him into a bucket, walked him down the hill, and released him near the lake. As luck would have it, a north wind had blown all the remaining ice up against my shore, so there wasn’t access to water. But I put the beetle on bare sand to let him warm up. He must have flown to my driveway; hopefully he can fly the last leg to the lake!

Since dispersing diving beetles have become a trend, it’s clearly my sign to write about them. Have you also encountered one recently?

Usually, you’d expect to see predaceous diving beetles swimming near the shallow edges of ponds and streams where there are plenty of aquatic plants to lay their eggs on, and few insectivorous fish. Their larvae are aquatic, but crawl out of the water to pupate in mud along the shore. Metamorphosis takes about a week, and they crawl right back into the water as adults.

Their continued surf-and-turf flexibility comes in handy if their little pond starts to dry up. Like most beetles, PDBs hide a pair of shimmering hindwings under an armored set of forewings called elytra. When all of their wings are closed, there’s a seam straight down the middle of their back. When open, the elytra look like the doors of the DeLorean in Back to the Future. The two cellophane-like hindwings pop out from underneath to flap away, with their large body and their hairy, paddle-like legs – adapted for swimming – dangling awkwardly.

The elytra don’t just hide more wings, they also trap a bubble of air next to the beetle’s breathing pores, which happen to be located on their rear end. The bubble is precisely sized to sustain their dive while not floating them back to the surface. Once the all of the oxygen has been gleaned from the air pocket (which reportedly takes somewhere between 10 minutes and 36 hours), the beetle swims up to the surface for a resupply. Sometimes they’ll climb fully out of the water and slather a layer of anti-microbial goo around their spiracles to keep their respiratory system healthy. Beetle larvae also have to return to the surface periodically to sip more air, which they store in their tracheal trunk. This handy storage vessel is similar to our windpipe.

Both the larvae and adults are fierce predators. PDB larvae have earned the nickname “water tigers” by ambush hunting with jaws open wide. Once they pounce, digestive enzymes flow through channels in their sharp pincers into the prey, turning the captive’s insides to goo. The larva then sucks out the prey smoothie. Although rarely seen because they tend to hide in the mud, the larvae occasionally bite humans. That their bites are described as “painful, but not medically important” is only mildly comforting. More comforting is the fact that they eat a lot of mosquito larvae.

Adult beetles are often credited with the same digestive enzyme injecting powers, but the most reliable sources I found described them as merely chewers and shredders. They often eat dead stuff, or they might sneak up on or even chase down insects, leeches, snails, tadpoles, small fish, AND mosquito larvae!

So what are these aquatic beetles doing on our decks, cars, and snow piles? Some species, especially those who tend to live in shallow ponds, change locations frequently, and often en masse! Has this dry spring forced them to leave shrinking pools? PDBs are also known to disperse to avoid parasites in their former home, predation, crowding, and competition from their buddies, and even a lack of plants.

Moonlight reflecting off water is a beacon for dispersing beetles, but this means that yard lights, cozy windows, wet roads, puddles, and shiny cars can lure them astray. These fast swimmers are slow and vulnerable on land, which benefits raccoons, skunks, snakes, and other little predators.

As they are flying around, predaceous diving beetles become somewhat waterproof, and may have trouble breaking through the surface tension of their hopeful new home. One way they resolve this is to exude “wetting agents” that breaks the surface tension, similar to dish soap. The more fun option is to dive in at high speed.

If one happens to dive toward your window, the shiny roof of your car, or some other reflective surface, at least now you know that you aren’t seeing June bugs in March.

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is 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 closed until May 1 to construct our new exhibit: “Anaamaagon: Under the Snow.” Our Winter/Spring Calendar of Events is open for registration! Follow us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.

A Vocabulary of Seeing

“Let’s start with the evergreens,” I told the small group who’d showed up for my tree identification program. Picking up a white pine bough, I plucked off a bundle of needles. “Pines cluster their needles in a group called a fascicle,” I lectured, “and they are held together at the base by a sheath.” Fascicle is one of my favorite botanical words, and I loved watching these newbies roll it around on their tongues. After years of formal training in plant identification, I’ve acquired a lot of vocabulary words that I don’t get to use very often.

I’ve also acquired some silly mnemonics for remembering plant ID. “Notice that these needles come in fascicles of five. That means it’s a white pine. W-H-I-T-E: white has five letters. Five needles, five letters. Also, the growth form of their needles makes white pines look like they have clouds on their branches, and clouds are white.”

White Pine needles come in fascicles of 5.

Folks humored me, nodding their heads in understanding. After examining a couple more evergreens, we turned to the jumble of bare sticks I had spread on the table. To most people it would look like a pile of junk. To me, it looked like a gathering of old friends with easy-to-see differences. The vocabulary started flowing.

Maples, ashes, dogwoods, and viburnums have opposite arrangement. Their twigs and buds sprout directly across from each other in pairs, while other trees place their buds and twigs singly, in an alternate arrangement. This is a good place to start your ID.

Sugar maple buds and twigs are oppositely arranged

Then we check out the buds more closely. Buds are miniature packages of new growth, pre-formed last summer, and just biding time until they can burst open in a flurry of new growth and elongation. Baby leaves, twigs, and flowers may all be crammed into the same bud, or special buds may hold the flowers. Tiny, tough, modified leaves cradle all that tender new growth, protecting it from desiccation. These bud scales give great clues to a plant’s identity. In sugar maples, the bud scales are a rich caramel color, and they are imbricate. Another one of my favorite botany vocab words, imbricate means overlapping like shingles.

These red maple buds have imbricate scales -- like shingles. They are also valvate -- meeting symmetrically like a clamshell. And ciliate margins with an edging of white hairs.

On red maples, the scales are imbricate, but there are fewer of them, and they are arranged symmetrically in pairs. If the scarlet buds and new growth on red maples aren’t enough it give away their ID, the buds also have distinctive “ciliate margins” of tiny white hairs edging each red bud scale.

I could see the gears turning as people squirreled away this information in preparation for the quiz. Shrubs always seem the most difficult to identify in winter, since they’re smaller, and lack the distinctive bark of a paper birch or red pine. But if you look closely, the ID is in the details.

Beaked hazel is one of the most common understory plants in these woods. Also known as “bear nut”, they are an excellent wildlife plant. From afar, they look like any other spindly shrub. Up close, their fuzzy, two-toned buds are quite handsome. Just two or three dark brown, imbricate scales clasp the bottom of the bud.

Beaked hazel buds and catkins identify the common shrub all winter long. Photo by Emily Stone.

The light brown, inner scales toward the tip are almost valvate (a term that means two symmetrical scales that come together like a clamshell.) They are also pubescent. The fine hairs that cover the scales serve to protect the bud from cold and dryness. In the spring—before the leaves unfurl—a tiny, red, octopus flower will sprout from the tip of the bud. In the leafless woods, wind can easily bring it a dusting of pollen. That pollen comes from tiny catkins on the hazel. All winter, the catkins are tan, fuzzy and compact. Any day now, they’ll elongate into pendulous yellow strings of flowers.

Early spring warmth has coaxed the tiny red flowers of beaked hazel to poke out of their buds. Photo by Emily Stone.

These buds and catkins all formed last summer, while leaves still clung to the trees. It’s in the tree’s best interest to make buds while the sun shines, and energy is plentiful. So there is only a brief time—just after spring bud break—when there are no buds to look at.

Fascicles. Arrangement. Imbricate. Ciliate. Valvate. Pubescent. Catkins. This language may seem complicated and excessive, but for humans, to name things is to see things, and vice versa.

In Braiding Sweetgrass, botanist Robin Wall Kimmerer philosophizes about the language of science. “Listening in wild places, we are audience to conversations in a language not our own. I think now that it was a longing to comprehend this language I heard in the woods that led me to science, to learn over the years to speak fluent botany. A tongue that should not, by the way, be mistaken for the language of plants. I did learn another language in science, though, one of careful observation, and an intimate vocabulary that names each little part. To name and describe you must first see, and science polishes the gift of seeing.”

As the students moved away to test their new knowledge, I hung back for a second, savoring the beauty of “see through” season in the leafless woods, and the words I have to see it with.

Author’s note: This article is reprinted from 2015.

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is 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 closed until May 1 to construct our new exhibit: “Anaamaagon: Under the Snow.” Our Winter/Spring Calendar of Events is open for registration! Follow us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.

Freezer Burn

Reaching into my chest freezer, I pulled out a quart-size zip-top bag full of dark green leaves. Or at least leaves that had once been dark green. The frilly edges of my kale were now a little pale in places, and ice crystals crunched brittlely inside the bag. Last summer I’d harvested grocery bags full of kale from my garden, blanched them briefly in boiling water, and then quenched them in two cold water baths. After stuffing a handful into a baggie, I rolled it from the bottom to squeeze out extra water and air, and firmly pressed the closure.

Despite my best efforts, several months in storage had led to freezer burn. Ice in the leaves had sublimated, turning from solid to gas without passing through the liquid state. The water that was once in the leaves had become the ice crystals in the bag. Unworried, I thawed the kale and chopped it finely to add to a soup simmering on the stove. Freezer burn isn’t dangerous to eat. It can affect the flavor of food, but I wasn’t counting on kale for flavor anyway.

The following day, I headed out for an afternoon walk. With bright sunshine, the temperature had risen just above freezing, but now a brisk wind was making the lengthening shadows quite chilly. As usual, I paused to admire the mosses growing along a steep, north-facing bank. On this day they weren’t very pretty.

Whole patches of moss were crinkled and brown, while others were brown at their tips, and some leaves were ghostly pale…not unlike my freezer burned kale. I nosed around a bit in the moss patch, taking photos and investigating the damage. Later, I emailed Joe Rohrer, Professor Emeritus of Biology, University of Wisconsin-Eau Claire. Joe taught a moss ecology workshop for the Museum in 2019, and will be teaching it again this October.

“Honestly, I can't cite a single academic paper on this topic,” wrote Joe. But he’s also been noticing chatter about this very topic in the moss-themed social media groups he’s part of. “The consensus seems to be that some mosses show winter dieback regularly but sprout new green growth in the spring. The moss gardeners see this a lot with Atrichum and Polytrichum species. The leaves of the previous year do seem to die, but new growth from the tip restores their green color. Other mosses just turn a rather ugly golden brown, such as Thuidium, probably similar to the red coloration we see in some vascular plants when they get winter sun but are shaded during the growing season.”

Uploading my moss photos to iNaturalist to identify them, I was able to confirm that the pattern he outlined seemed to hold true on my driveway.

“My guess is that drying out is probably more harmful than freezing temperatures,” Joe concluded.

And I agreed. One of the benefits of the Subnivean Zone, which never had a chance to truly develop on my driveway this winter, is that a blanket of snow holds moisture close to the soil. According to horticulturists, winter burn is caused by low soil moisture, freezing temperatures, and blowing wind. Not only does that magical space hold the temperature steady near 32 degrees, it also eliminates windchill, and provides a high humidity habitat. Without it, moisture sublimates from the moss leaves just like from my kale.

It's not that mosses haven’t prepared for this. As drought sets in, their cell membranes shrink like vacuum-sealed freezer bags. This winter has been especially rough, though, with many nights below freezing without snow on the ground. Hopefully the mosses were able to synthesize a big enough supply of enzymes for cell repair to manage the damage from this weird winter.

Next to that sad patch of moss were several rosettes of fern leaves. Evergreen wood fern doesn’t die back in the fall. Instead they flatten to the ground and let snow cover them. Concentrated sugars act like antifreeze in temperatures 5-10 degrees below freezing, and special proteins keep them from being damaged as temperatures plummet further. Even in a normal winter, these leaves never stand back up. They are replaced by fresh, new leaves in the spring. But for several months they can continue to do photosynthesis—while leaves are off the trees—and give the plant a head start on new growth. Maybe.

The tips of the evergreen wood fern fronds near my sad mosses are curled up and look dry. Water is essential for photosynthesis. I can’t imagine they are very productive right now, and I wonder if they will even recover if it eventually rains.

Farther up the road, I stopped near another nearly vertical bank. Dozens of wintergreen plants poked stiffly up above the dry brown leaves. They looked pale and dehydrated, just like the ferns. Would their waxy leaves be tough enough to survive the dry cold? They are well-adapted to hunkering down in the Subnivean Zone and even photosynthesizing there. These many weeks of exposure to dry cold must be challenging, even to them.

I wasn’t looking for wintergreen, though. One of my favorite spring flowers, trailing arbutus, grows on this bank, too, but spotting them is always a challenge. Finally, I glimpsed the brighter green, broader leaves peeking out from under the duff. They didn’t look freezer burned. Perhaps the secretive, ground-hugging nature of this little plant is a way to survive winters just like this one. Soon they will bloom, and I’ll plant more kale, and most of the mosses will recover. Soon, this weird winter will be over.

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is 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 closed until May 1 to construct our new exhibit: “Anaamaagon: Under the Snow.” Our Winter/Spring Calendar of Events is open for registration! Follow us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.

Bark Eaters

“Who’s eating my trees?” asked a participant on a hike last week. I’d been wondering the same thing! A few weeks ago I noticed creamy colored exposed wood on several small maple trees along my driveway.

“Why do animals even eat bark?” someone else asked. Good question. Most bark is composed of tough, dead, dry cells that are not very appetizing. Those cells are made of lignin, which makes wood rigid and is very hard for digestive systems to break down. White-rot fungi and a few bacteria are the only organisms who can consume lignin using specialized enzymes. Bark also contains tannins, which are bitter tasting chemicals that can inhibit digestion.

Unappetizing outer bark is how trees protect their slightly more appealing inner bark. In a tree trunk there are several layers of different cells, including xylem and phloem. Xylem, which is dead at maturity, carries water and minerals up from the soil. Old xylem becomes what we think of as wood. The living phloem carries sugars down from the leaves. They have a layer between them called the vascular cambium, which creates new xylem and phloem cells. Cambium is made of undifferentiated cells who can become anything - like stem cells. These three layers are considered the inner bark.

The living cells of the inner bark contain complex carbohydrates, sugars, and minerals. Right now, when the maple sap is running through the xylem, the inner bark is extra sweet! Even in the dead of winter, inner bark was a source of food for the animals who can access it…and digest it.

Porcupines are one likely culprit in the decortication (bark removal) of my trees. The bottoms of their feet are hairless and covered in a pebbly texture that improves their grip. Long, curved fronts claws also aid in tree climbing, along with bristles on the underside of their tail. To get at the most nutritious parts of a twig, porcupines will balance out toward the terminus of a branch and nip off its end using their self-sharpening incisors. Turning the stick around, they nibble off all the most tender twig tips and buds and then discard the rest. Sometimes you’ll see porcupine tooth marks on bigger branches, too, or even the trunk.

With long claws and several other adaptations, porcupines are able to eat seemingly unappetizing tree bark. Photo by Emily Stone.

Hemlocks are their favorite winter food. As spring progresses, porcupines nibble on a buffet of different trees and plants, making sure to eat each one at their point of peak nutrition. Even this careful food selection wouldn’t be enough without one more adaptation: porcupines have an extremely long large intestine filled with microorganisms who produce lots of enzymes. This extended digestion allows porcupines to extract more nutrients from their food.

Reading about porcupine digestion made me curious about their cousins, the beavers. Now, there’s no way that a beaver could have nibbled the bark on the twigs of trees still standing along my driveway, but these two big herbivorous rodents have quite a bit in common, and some important differences. An article in the Canadian Journal of Zoology suggests that beavers don’t chew their food quite as well as porcupines, but make up for it by having a small intestine that’s 70% longer! The porcupine has a longer colon, though, which allows them to absorb more water from their food. That makes sense, given their different habitats.

There’s one other big difference: beavers engage in coprophagy. Beavers will re-ingest their first round of poop so that they can have another go at extracting all possible nutrients.

Beavers share the trait of coprophagy with another bark eater: bunnies. Rabbits and hares have short digestive tracks, so they combine a good microbiome with coprophagy to enhance digestion. Both rabbits and hares eat their first round of soft, greenish cecal pellets, and then leave behind fecal pellets that look like M&Ms made of sawdust. This allows them to eat twigs and inner bark in the winter. Of course, they focus on the bark of small stems at the height of the snowdrifts…not in the tops of trees.

Voles also eat bark low to the ground. These little rodents like to hide in the subnivean zone under the snow and nibble on bark in relative warmth and safety. They can damage trees, even girdling and killing them. Voles have a specialized pouch called a cecum at the beginning of the large intestine that provides a place for food to be fermented. They may also use coprophagy to help absorb certain nutrients.

In comparison, deer have the most complicated gut for digesting bark and twigs. They are ruminants with four stomachs, like cows. Microorganisms in deer’s rumen break down tough materials, aided by them regurgitating and chewing their cud until it’s broken down enough to move on to the rest of the stomachs. Deer might strip bark off a young tree higher than a hare, but not high in the treetops like I’d observed.

So, who was the bark-eating culprit in the trees along my driveway? Judging by the tiny tooth marks, and my most commonly seen neighbors, they were gray squirrels. Squirrels have sharp teeth and excellent climbing skills just like porcupines, and can venture out onto smaller branches to nibble on the most tender bark. Squirrel tooth marks are less than 2 mm wide, while porcupines’ teeth are two to three times that big.

The tiny tooth marks high up on a sugar maple sapling are likely the work of a hungry gray squirrel. Photo by Emily Stone. 

Discarded bark strips litter a log below the decorticated tree.

Recent research suggests that special gut bacteria help gray squirrels extract calcium from tree bark. This adaptation might be what’s allowing gray squirrels to outcompete the native red squirrels in Great Britain, where gray squirrels were introduced. Our native red squirrels have been observed eating bark less frequently than grays, but they are smart enough to know that making a small incision in sugar maple bark this time of year releases another one of bark’s sweet secrets.

Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is 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. Our exhibit: “The Northwoods ROCKS!” is open through March 9. Our Winter/Spring Calendar of Events is ready for registration! Follow us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.