The Beetle and the Invisible CityOn Costa Rica's Turrialba Volcano, a journey into the living systems beneath the world, Part II.
This is part II of Turrialba Volcano and the Infrastructure of Everything. It continues on Notes from the Road here. At night, the rain comes down hard at Rancho Naturalista—so hard that the four other guests cancel their plans for a guided night walk. Teylor, their guide, ends up with nothing scheduled and eggs me on to join him. I grab my umbrella and headlamp and find him by the narrow trail leading into the trees. The sound of the rain is deafening. It doesn’t quite drown out a Mottled Owl hooting in the distance. While walking through the forest, Teylor’s headlamp catches a beetle on a giant tree stump hanging over the slope. It is already dead, fixed in place by the fungus that has overtaken it. “It’s ironic,” Teylor says, lifting his flashlight toward the beetle. “It’s a fungus beetle. They specialize in eating fungus. But sometimes it’s the fungus that wins. They’ve killed the beetle, and now they’re eating him.” The beetle is Cypherotylus vicinus. As a larva, this little guy lived buried inside rotting logs or hidden in the fungus-loaded leaf litter on the forest floor. Just chewing slowly, day after day, completely hidden away in its own private fungal universe. The grown-up fungus beetles don’t change their diet—they’re still total fungus addicts, still mycophagous like before. The difference is that now you actually see them. They wander out onto the forest floor and move across dead wood and leaves. They eat whatever fungus is exposed—slime molds, small mushrooms, thin coatings on logs. They don’t search so much as bump into food as they go. Adult Cypherotylus vicinus have bright, striking coloration—red and orange, black and white. Here is an important rule of the forest: if you live on the ground and are colorful, you’re probably poisonous. But if you’re colorful and slow, you’re probably deadly.
Vicinus, like other pleasing fungus beetles, are absurdly slow. Fungus-eating animals are often chemically interesting. In the case of vicinus, whatever makes them deadly likely comes from what they eat: processed fungal compounds weaponized into first-rate defense. As we study the crime scene more closely, we can see that the fungus itself is like a miniature forest of white stalks with pink heads. The center of this stalk forest appears to be the beetle. The fungal growth has burst through the seams of the hardened body and now spreads outward across the scene of the crime. What happened here? The vicinus beetle was probably just doing what he always does, trudging along at the pace of an elderly sloth, stopping here and there to munch some fungi. Somewhere along the way, he must have brushed up against spores of a cordyceps fungus. You might recognize the word cordyceps from The Last of Us, the HBO series starring Bella Ramsey and Pedro Pascal, where a fictionalized cordyceps infects humans, hijacks their brains, wipes out individual will, and turns people into zombies whose only role is to spread the fungus. The human part is fantasy. The basic mechanism is not. Cordyceps infect the beetle because the beetle moves, and it infects beetles like vicinus because they spend their entire lives among fungi: ready-made transport, the way a burr catches in mammal fur. After a few minutes of studying the crime scene, Teylor moves on, leaving the stump behind and continuing down the trail.
Beetles represent the most expansive exploration of animal life on Earth. About 400,000 species have been described, but coleopterists believe there are over two million beetle species in the world. They account for a whopping 40% of all known insects and 25% of all described animals on Earth. These insects occupy nearly every place where there is organic matter. They thrive in forest canopies and on desert sands, in river margins and rotting logs, deep soil and inside animal burrows. They basically live in almost every land and freshwater habitat. If coccolithophores represent a small number of species that have global reach on the biosphere, beetles are the opposite. They have global impact because of their diversity, their dazzling specialization. The tiniest beetle in the world is a featherwing beetle. It’s so small, at just 325 micrometers, you can just barely see it with the naked eye. I once saw a pair of titan beetles, almost seven inches long, not including legs. But I was absolutely horrified to learn that when I approached them, they could fly. The clanking sound of their stiff mechanical wings is the soundtrack to my own personal hell. Some beetles live their entire lives inhabiting just one plant species. Others show up just when something is at a precise stage of decay, like when wood softens. They disappear as soon as it collapses into soil. Their body plans follow their specialized functions. Some are shaped with flattened forms to slide beneath bark, others are heavily armored to push through soil. Some are elongated to navigate tight crevices, and then, of course, there are those oceanic-like streamlined swimmers that patrol the margins of lakes and marshes. Together, these millions of beetle species form a living architecture. They aren’t interchangeable. Most of them only do one thing, and often only briefly. Dead material gets reduced. Nutrients get moved. Energy goes up the food chain. It happens everywhere, constantly, without any coordination. A few weeks ago, I was walking the sand dunes of Death Valley after dark when I noticed something tiny lumbering across the sand. I lay down to take a closer look, hoping to send a photo to Jane and Kellan to compete with their cat pics. It was a pea-sized creature covered in long white hairs, making it look like a mythical mammal in miniature. It was Edrotes ventricotus, the Hairy Robot Darkling Beetle. This species comes out at night and slowly munches the scattered desert debris into soil. They are so specialized, they live only among the loose sand of the Mojave and Sonoran deserts.
Biologists will often say that beetles are the most important organisms on Earth. What makes them so critical is how their huge numbers explode into hyper-specialized roles, and how that specialization keeps ecosystems stable and the carbon cycle operating correctly on land. Without beetles, carbon gets stuck in frozen ground, locked in wood, pooled in waste, or dumped out fast when forests crash. Beetle diversity keeps those failures from happening all at once. Different species show up at different moments: one for a particular fungus, another for a certain stage of decay, others for dung, seeds, carrion, or soil. The constant movement of carbon in the natural world is essential for life; keeping too much of it out of the atmosphere is critical. But beetles do more than stabilize climate. They keep soil working, stop forests from filling up with debris, hold pest outbreaks in check, and make sure nutrients make it back to plants. Without them, entire ecosystems would fail. Among those ecosystems is our global agricultural output. Our crops are assisted by fertile soils renewed by beetles. In fact, over 95% of all crops depend on healthy soil, amended by beetles and other insects, fungi, and microbes. Dung beetles are considered essential in pasture productivity; they are among the primary controllers of livestock parasites like flies and nematodes, and they are essential in returning animal dung back into the soil. Beetles even act as pollinators to some of our crops, including fruit trees, spices, palms, and magnolias. Entire forests persist because beetles keep many of the systems from falling completely out of control. The biosphere, and the basic underpinnings of human civilization—from food security to clean air and water, as well as climate regulation itself—rely disproportionately on these six-legged hidden workers. Farther up the trail, Teylor hoots something at me, which I can barely hear. I’m fussing with my headlamp, which flickers and goes dim. As I turn on my phone’s flashlight as a backup, my umbrella catches the dirt wall beside the path, scraping a thin layer of wet soil. In the blue light of the phone light, I can see pale threads running through the dirt. The same ones I remember seeing while digging for worms as a kid in Minnesota. The same filaments that fed the beetle. The same network that eventually consumed it. The same fungal network upon which all life depends. Part III continues in two weeks. Notes from the Road is free today. But if you enjoyed this post, you can tell Notes from the Road that their writing is valuable by pledging a future subscription. You won't be charged unless they enable payments.
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