plants communicating with plants --5/14/25

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Today's selection-- from The Light Eaters by Zoë Schlanger. The surprising interactions of plants with other plants and with animals:

“By now I’d learned from Rick Karban and his sagebrush about plant-to-plant communication, the elaborate exchange of chemical signals that warn other plants about impending threats. I understood that this quiet speech was everywhere, passing easily beneath our perception, a form of communication requiring neither sound nor movement. A world of meaning was adrift on the air. Yet for the most part, the study of plant-to-plant communication seemed to focus mostly on alarm calls: who warned who, and when. This made sense; preparing for an attack is crucial to survival. But with this much power to transmit meaning, warnings couldn't be the only thing being passed around, I thought. There had to be more to plant communication than alarm calls. This, I learned, was apt—there was much more being discussed. But what I didn't consider, until I came across it, was that plants hardly keep the dialogue to their own kind. They regularly cross the species divide.

“Indeed, the relationships plants have with other plant species, and even with animals, is a tapestry of dynamics that run the gamut from reciprocal to exquisitely antagonistic. Often it is hard to tell the difference. The field that studies this is flatly called ‘biocommunication,’ but that seems too tidy for the complicated pile of interspecies relationships being uncovered today. As I fall into the world of biocommunication, I get the sense that the rule of life is unruly mixture. Everything, it seems, is impacting and altering everything else. I'm reminded of a phrase used by theorist Donna Haraway, who writes that our lives, whether we notice it or not, are a ‘rich wallow in multispecies muddles.’

“Consuelo De Moraes, the ecologist who discovered how dodder vines select their prey, lives squarely inside this muddle. She sits on the edge and watches, squinting, as species upon species interact. In fact, she seems preternaturally attuned to seeing meaningful interactions where scientists before her have seen absolutely nothing. She is a strictly scientific kind of person, and there is a no-nonsense clarity to her speech. She won't tell me about anything she isn't sure she can replicate or doesn't feel confident will make it past peer review. But she also feels capable of wonder, in fact uses it as a primary research tool. Her sense of rigor makes her dispatches from the world of multispecies muddles feel reliable, and all the more gobsmacking for it.

“De Moraes speaks to me from across her desk at the department of environmental systems science at ETH Zurich, where she is silhouetted by a gallery wall of butterflies pinned inside square picture frames. These are the adult forms of the caterpillars she studies. She specializes in insects, plants, and viruses that often layer their lives upon one another in ornate ways. For example, in the 1990s, she was studying the triangle of drama between corn, caterpillars, and wasps. First a caterpillar chews a corn plant. The plant notices this, and samples the combination of saliva and regurgitant the caterpillar leaves behind on its leaves; now the plant knows the caterpillar's species—or at least which species of wasp it needs to come parasitize it. The plant then releases a finely tuned chemical gas. Within an hour, the correct wasps arrive. The wasps, no doubt appreciative of the ideal scene before them, insert their needle-like appendages into the caterpillars' bodies, injecting their eggs inside them. When the eggs hatch, the wasp larvae use their especially oversize mandibles to eat the caterpillars from the inside out. They then spin their Tic Tac-shaped cocoons, which they glue to the emptied husks of their caterpillar. The result is a green wormish form bristling with white silky spines, like hedgehog quills made of felt. And thus the plant attempts to save itself. De Moraes discovered this behavior in corn, tobacco, and cotton in 1998.

Dandelion flower under both UV light coloration (left) and visible light coloration (right). UV coloration in flowers has evolved to attract pollinators with vision in the ultraviolet range.

“Two decades later, De Moraes noticed little bite marks on the leaves of some black mustard plants she was growing in a greenhouse. The marks looked like tiny crescent moons, always a tell for a bumblebee mouth. But why were bumblebees biting plants? She kept watching.

“The bumblebees, she realized, were starving. They'd been flying around the closed buds of mustard flowers for days, but no bloom had yet opened. If they didn't slip their tongues in a pool of sugary flower water soon, they would begin to slow down, their bodies desperately trying to conserve calories. Eventually they would land on the dirt, crawl a while, and die. The poor bees; their timing was all wrong. The flowers weren't due to open for another month. It wouldn't do. The bees, she saw, began to bite the plants' leaves. The next day the flowers bloomed. The bees drank the nectar and survived.

“Interesting, De Moraes thought. Bees don't eat leaves. There seemed to be no good reason to waste precious energy on something that wouldn't feed them. But here they were, biting them regardless. There were moons all over the place. Someone must have noticed this before, she thought. 'And then you do this literature search, and it's like, how did they miss this?’

“She set up an experiment with all the proper controls and found that bees biting plants made their flowers bloom as much as thirty days earlier than they would otherwise. Obviously, the bees benefit herebut, Consuelo found, so do the plants; they bloom in time to have bees around to pollinate them. Timing in nature is like that: all species rely on other species in one way or another. If they're out of sync, everyone loses. Survival depends on having a way to communicate across the species divide.

"’One of my students sent me photos of her spinach salad with these half-moon shapes,' De Moraes said. ‘We would never look for it before, but now we're looking around and going, oh my god, bee damage. After you know, your mind starts seeing that thing all the time.’

“Common bumblebees, she's found, can tell at a distance whether a yellow monkey flower will have lots of pollen for them or not, by the scent of a certain floral volatile compound that translates, in a bee brain, to ‘heaps of pollen.' But making heaps of pollen takes a lot of resources. So the monkey flower has developed a shortcut. It recognizes the rules of this pre-screening process, and instead of making extra pollen, will exude the volatile anywa—-in essence, it will lie. The bumblebee, now duped, will arrive to disappointment. Either way, the monkey flower got what it wanted: a bumblebee to dust with pollen. The monkey flower is an excellent liar.

“With biocommunication, it's monkey flowers all the way down. De Moraes talks about the ‘arms race’ of insects, plants, and viruses, each outsmarting the other and being outsmarted at turns. ‘Everybody is trying to survive. All of them.’ She often laughs as she explains her findings, as if experiencing her own amazement at the results all over again. I get the sense she isn't as wedded to this vision of nature as a battlefield, but it's a metaphor near at hand in all of science since Darwin, so she uses it.”

author:	Zoë Schlanger
title:	The Light Eaters: How the Unseen World of Plant Intelligence Offers a New Understanding of Life on Earth
publisher:	Harper
pages:	138-141