Frigid and Flourishing: Freeze-Proof

This post series opened with Part 1, an exploration of some snow-dwelling lifeforms.

The sun sets on the Yukon Territory’s Porcupine River, slowly melting into a far-off, lazy oxbow, pouring its tangerine light one last time over the endless, icy stillness. It’s just before four in the afternoon, the New Year is soon approaching, and it is cold. Very, very cold. As the blue above dims, and the blinding mango creamsicle spectacle comes to a rapid close in the west, you can almost hear the river ice creak and wince in anticipation for what’s coming. It only got up to 20 below today. The nights have grown large this time of year, and cruel. First light won’t come for what seems like eternity, and by then, the air will be a devastating -60 degrees Fahrenheit. Cold enough to kill exposed human skin in a handful of minutes. Cold enough to turn even antifreeze-laden gasoline into flammable slush. Cold enough for breath to stiffen in an instant, collecting as a growing layer of biting rime on every hair on one’s own face; eyelashes, eyebrows, the whole bit. In the growing dark, nothing moves. Chickadees settle into tree cavities, and rapidly begin burning through the fat reserves they gained during the day’s feeding, all just to keep warm. Caribou huddle and lay low. Ptarmigan wriggle into the snow (surprisingly, for insulation), stoking their metabolic fires with a crop pouch full of food. To survive the night, Life winds down everywhere, becoming motionless and dipping unnervingly near death in a desperate attempt to stay alive.

Well, everywhere except within the cramped, moist layers of bark of the naked balsam poplars lining the riverbank, stony and brittle with the cold. In there, somehow, life stirs, pushing and wriggling its way through its frozen, wooden den. It’s a tiny beetle grub, a larva of the northern red flat bark beetle (Cucujus clavipes puniceus), no longer than the graphite tip of a well-sharpened pencil. It has no blanket of thick fur or fluffy feathers, no fat-powered metabolic oven to keep it warm. It is a bare-assed worm, twenty feet up in a barren, ligneous spire, sandwiched between the unrelenting sadism of the Arctic atmosphere and a block of nearly lifeless wood….possibly the worst possible location for cold exposure. And yet, it is comfortable, its teeny body barely noticing the silent, breath-stealing chill invading from outside the bark.

Why? Because when the frosty grip of boreal death extends its hand, the larval red flat bark beetle tells it to fuck off.

Not bad for something that looks like a condom filled with urine-flavored Jello.

The red flat bark beetle ranges across a huge latitudinal swath of North America; from the Carolinas north and west into northern Canada and Alaska. As its name implies, this insect is the opposite of a claustrophobe, spending its entire life squeezed under the bark layer of trees, living or dead. They are particularly fond of deciduous trees like poplars, ashes, and oaks. In their mature state, red flat bark beetles are significantly more attractive creatures. The adult beetles are a bit smaller than their grub form, and have a clean, rectangular, distinctly compressed shape, all the while appearing to be made out of a rich, well-oiled mahogany.

Those wing cases double as a cellarette.
Photo: Mark Leppin

Of course, there are LOTS of bark beetles in the world. Split open any given piece of rotting lumber while out in the forest, and you’ll likely see at least several species of adult bark beetle scuttle out of the light. If you take a closer look, you might see larvae of additional species boring sinuous trails into wood itself. Dead wood and beetles go together like chicken and waffles. In that regard, the red flat bark beetle isn’t all that special. But not all bark beetles have mastered survival in otherworldly winter conditions like this species has.

Most insects tend to not want to tangle with the full brunt of subzero winter conditions. They’ll hibernate in warm, huddled piles until warm weather returns, or, as in the case of monarch butterflies or green darner dragonflies, they’ll simply migrate to more amiable southern climes for half the year. But the red flat bark beetle holds its ground, staying put in its insulation-deficient home, even in the face of insane temperature extremes. It doesn’t have a death wish, and it’s no haggard, masochistic badass. The larvae of these beetles overwinter through a harsh, Hothian hellscape….well…because they have a superpower up their sleeve.

They are really, really hard to freeze.

Red flat bark beetles act like miniature Wim Hofs because they have evolved a unique strategy for dealing with winter; that is, producing a number of chemicals in their bodies that make them exceptionally difficult to crystallize. They winterize themselves, like you would your home or car, and begin saturating their tissues with specific compounds that they make directly within their own bodies. As summer comes to a close, the beetles begin to create and store proteins that have potent antifreeze properties, thought to work by migrating and sticking to places in the body where ice crystals are likely to form. As fall drags on, the beetles start producing glycerol, which, like the ethylene glycol found in a jug of Prestone antifreeze, chemically interferes with the ability of water molecules to form a crystal lattice…making the freezing point of whatever it’s added to to drop like a rock. The western subspecies, Cucujus clavipes puniceus, which ranges much further north (into Alaska and the Yukon) than the eastern subspecies (which is more centered around the Eastern U.S. and Great Lakes region) produces a great deal more of these antifreeze compounds.

When the really cold temperatures hit, the beetles will dehydrate themselves, avoiding freezing by purging themselves of the thing most likely to freeze inside of them: water. These beetles use chemical aids to alter themselves in such a way that they can triumph over exceedingly difficult situations, which, in a way, is a method I recently employed to make it through watching Sarah Palin endorse Donald Trump for President.

*quietly in the background*
“…how ‘bout the rest of us? Right wingin’, bitter clingin’, proud clingers of our guns, our god, and our religions, and our Constitution…”

This jumping through stepwise biochemical hoops produces a kind of extreme “freeze-avoidance”, where the bark beetle doesn’t engage in behaviors that make it less freezable, but directly changes the composition of its body to provide freeze immunity. Without this suite of in-house developed potions and techniques, a brief brush with just a brisk, Arctic Circle autumn evening would leave these larvae stiffer than a Solo in carbonite.

So, how does the freeze-free solution of the Cucujus bark beetle hold up against the most intense possible side of the low Arctic winter months? How far can they stand the mercury to shrink? Well, there’s a good way to find an answer to that question, and it involves sticking thermocouples on some very unhappy beetles, throwing them in glass containers, and dipping those containers in an alcohol-water cooling bath….and then waiting for the cold to do its work.

It turns out that as the temperature drops, the red flat bark beetle larvae tend to do just fine staying still and enduring the chill without any major physiological changes until about -75 degrees Fahrenheit (-60 degrees Celsius). Right around there, at temperatures about as cold as it ever gets in this far northern habitat, something remarkable happens to many of the beetle larvae.

The bastards turn to glass.

Well, technically speaking, they “vitrify”, meaning that instead of allowing ice to form and crystallize all the fluids in their soft, water balloon bodies, they congeal into a stable, non-crystalline, solid state…or a “glass.” In the case of the beetle larvae, this is less like becoming an elegant, clear wine glass, and more like morphing into the world’s least appetizing flavor of Jolly Rancher. In this bizarre state, the larvae can avoid freezing outright down to an unreal -238 degrees Fahrenheit (-150 degrees Celsius) like a bunch of indestructible Werther’s Originals. That being said, just because these larvae manage to keep from turning to ice, it doesn’t mean they survive the ordeal. Only a tiny fraction of those subjected to temperatures below -94 degrees Fahrenheit (-70 degrees Celsius) continued to live after being rewarmed to room temperature and brought back out of their glass form. At this point, it appears as though the red flat bark beetle’s physiology is capable of amazing feats in extreme temperatures that it would likely never encounter in the wild, but in the end, it’s as if the beetle’s freeze-avoiding ego writes checks its body can’t cash.

A similar winter survival adaptation can be found in another species of beetle: the roughened darkling beetle (Upis ceramboides), which is also found in northern North America, as well as across the Eurasian subarctic. However, these insects technically become beetlesicles at around 20 degrees below Fahrenheit, but apparently produce a complex sugar-derived polymer called xylomannan that allows survival at much, much colder temperatures, possibly by keeping the ice crystals that form in the fluid between cells from actually piercing and rupturing the thin membranes enveloping these living cells. This full-frosty, “freeze-tolerant” method of survival evolved independently and in parallel with the “freeze-avoidant” measures taken by the red flat bark beetles.

A rare photo of Upis ceramboides heroically taking on the worst winter can throw its way.

All this side-stepping of a grim, glacial demise would surely be a welcome addition to the repertoire of skills held by many other bark beetle species, including some that are common prey to both the predaceous young and adult red flat bark beetles and their close relatives in the genus Cucujus. Among them are the mountain pine beetles (Dendroctonus ponderosae), a member of the weevil family (Curculionidae) found all over western North America, from British Columbia south into Mexico. Mountain pine beetles feed and reproduce under the bark of a number of species of pine tree found in the region. These beetles don’t have the extreme cold tolerance found in either the red flat bark beetles or the Upis beetles, and periodically succumb to periods of exceptionally cold weather. Traditionally, this has been a good thing for the ecosystems they inhabit, because mountain pine beetles have an impact on their host trees that is incredibly disproportional to their small size. The beetles lay their eggs inside the bark layer, and the young feed and bore into the sensitive, life-giving sap layers deeper into the tree. The beetles also introduce a variety of pathogenic fungus into the tree, and the combination of beetle infestation and fungal infection messes with the tree’s nutrient transport system so badly, that in a number of weeks, the tree will die. Under normal, moderate infestation conditions, this actually works out well for the forest. Unhealthy, vulnerable trees are put out of their misery before any others, and new, vibrant forest grows up in their place, and the beetles manage to contribute to the forest’s sensitive nutrient cycle. Occasional spikes of bitter cold in the winters would assist in keeping beetle numbers low. The forest gets spruced up (so to speak) every so often by beetle culling, the beetles never have a chance to get too numerous and overwhelming due to a cold snap here and there. Everything in perfect harmony, right?

Sure. But things go to shit pretty quickly when you throw in drought (which stresses out the trees and makes them acutely less likely to handle beetle infestation well) and incrementally rising temperatures, which make cold snaps occur less frequently…if at all. If this double-pronged scenario sounds familiar to you, then you’ve probably seen what’s been happening to the expansive evergreen forests that blanket the Mountain West over the past several decades. Climate change, through warmer, shorter winters and hotter, drier summers has allowed the beetles to run roughshod over North America’s pine forests. And the effects can be observed in all their depressing glory anywhere in the Rockies, as endless stands of what was healthy, verdant pine forest as little as five or ten years before, has been replaced by the rusty brush of thirsty, coniferous death similar to the remains of a discarded Christmas tree in a late-January dumpster.

These aren’t happy little trees from Bob Ross’s “Red Period.” These are standing corpses, victims of an insect unchained.

I’ve seen these forests riddled with “beetle kill” first hand, having spent seven years of my childhood living in remote central Idaho. I remember seeing the first notable brick-colored speckling in the high-elevation forests in the Sawtooth Range at the close of the 90s, and within a handful of years, green trees seemed to become a minority. The current outbreak of mountain pine beetles, no longer challenged by stiff winters, robust plant defenses, or any barriers to explosive reproduction, is of epic proportions, but more recently, there are signs in certain regions (like Colorado) that localized beetle numbers have fallen…but potentially only because so few suitable trees remain for exploitation.

Perhaps the mountain pine beetle would complain that it literally shivers in timbers, unlike the winter weather champion beetles to their north, but thanks to the consequences of human-driven climate fuckery, they might not have any use for potent freeze-mitigation adaptations for a long, long while.

Image credits: Intro composite of beetle in ice bath (from images here and here), larval red flat bark beetle, beetle kill forest vista

© Jacob Buehler and “Shit You Didn’t Know About Biology”, 2012-2016. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Jacob Buehler and “Shit You Didn’t Know About Biology” with appropriate and specific direction to the original content.


1 thought on “Frigid and Flourishing: Freeze-Proof

  1. You talk about the low survival rate of beetles that are rewarmed after vitrifying, but you don’t discuss how that rewarming was done. (Maybe it is in one of the links but I didn’t follow them.) This seems like a lot of evolutionary work to produce a feature with such low success – rather doubtful I think. Waiting here in the frozen midwest for spring to arrive I realize that it doesn’t just come like being thrown from liquid N temps into room temps (wish that it did) but the temperature rises in fits and starts over a month or more. Some days come up to freezing for a high and then drop down at night and then this is followed by a day with a high 5 degrees higher. I suspect that if you warm your beetles gently more of them will survive.

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