Insectopedia (51 page)

The sounds can’t be arbitrary, he decides. These animals are not simply following their instincts. “The musician in me cannot help but hear more.” In fact, the musician in him understands human music as a parallel expression to these sounds, as the expressive modality that brings people closest to the ways in which other forms of life communicate. Music suggests organization, not simply sound, and he hears the pond “saturated with an intelligence emergent from the very fullness of interconnection.” He begins to hear the pond as a kind of superorganism, a transcendent social “mind” created from the autonomous interaction of all the life within it, terms not dissimilar to those used by complexity theorists to describe the nest colonies of the eusocial insects (ants and termites, some bees and wasps, some aphids and thrips).

As I read these ideas in the liner notes for “Chaos and the Emergent Mind of the Pond,” I start to understand that the soundscape is more than a recording, more even than a composition. It is also a research method, one that flows easily from a principle of wholeness. The soundscape encounters its piece of the world as a totality. In this, it’s quite unlike scientific investigations that begin their search by isolating individual elements. The method is different, and not surprisingly, the outcome is different too. Something else surfaces. Let’s not stay deaf to its music.

“For a long time,” David Dunn told me, “that was enough.” He composed soundscapes to sensitize his audience to the acoustics of the natural world, to stimulate the recovery of older, lost sensitivities, and to offer
more intimate relationships with other life-forms. But climate change changed that too. The dying forests posed the question of responsibility with new urgency. Like many in the midst and wake of disaster, he found himself wrestling with the desire to do something effective, something, as he put it, “to diminish my own sense of tragedy and depression.”

The piñon die-off was no anomaly. As temperature zones have shifted in the past decades, insects have shifted with them. Swift, numerous, and astonishingly adaptive, beetles, mosquitoes, ticks, and others have taken advantage of new conditions and newly expanded habitat ranges with spectacular results. One widely publicized effect is the unwelcome appearance of insect-borne diseases in unexpected latitudes and altitudes (Lyme disease in Sweden and the Czech Republic; West Nile virus in the United States and Canada; dengue fever as far north as Texas; malaria in the East African highlands).
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Another is the unprecedented deforestation that’s struck the boreal forests of Siberia, Alaska, and Canada, the coniferous forests of the southwestern United States, and the temperate forests of the Midwest and Northeast.

The details vary, but the dynamic is well established. Confronted by regional increases in winter and summer temperatures, decreases in precipitation, and the reduction in the duration of freezes, plants and insects have fallen out of step—despite often having co-evolved for millennia. The animals adapt at a rate far more rapid than that of the trees. The beetles accelerate: they eat more; they develop faster (some species move to adulthood in one year rather than two); they reproduce quicker and survive longer. Their numbers explode.

The same conditions of higher temperature and lower rainfall stress the trees. As drought intensifies, their metabolism breaks down, and their defenses weaken. Their established strategy—the migration of populations out of the higher temperature zones over generations—is simply too slow. Temporalities are out of joint. The forest comes apart. The trees are overwhelmed long before they can escape to a place less hospitable to the insects.

The result has been a catalog of destruction. Since the early 1990s, spruce bark beetles have caused the death of 4.4 million acres of Alaskan boreal forest. In the same period, the mountain pine beetle has moved into 33 million acres of forest in British Columbia and caused major
damage in Montana, northern Colorado, and southern Wyoming. Long-term predictions are suitably apocalyptic. One North American scenario envisions a continent-wide invasion of bark beetles radiating from British Columbia to Labrador and down into the forests of eastern Texas.
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David and his collaborator, the University of California physicist James Crutchfield, an expert in nonlinear complex systems, describe the mechanism at work here as a “desynchronization of biotic developmental patterns.”
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They investigate it in a new project imagined through the logic of the soundscape, a scientific inquiry symbiotic with
The Sound of Light in Trees
that doesn’t so much look at climate change as listen to it.

For several decades, research on insect behavior has been dominated by chemical ecology, the study of the effect of chemical cues on ecological interaction. In his fascinating account of a life among insects, Thomas Eisner, pioneer and undisputed giant in the field, documents the discoveries: the bombardier beetles that spray scalding benzoquinones when threatened; the female
Photuris
fireflies, which procure defensive chemicals by consuming male fireflies of a different genus; the beautiful female moth
Utetheisa ornatrix
, which discriminates among sexual partners according to the finest calibrations of pheromonal scent; the defensive toxic-vomit response of sawfly larvae and grasshoppers. The stories seem infinite, and so, too, Eisner makes clear, do the opportunities for further research.
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Chemical ecology has proved to be an overwhelmingly fertile field for insect studies. In particular, tremendous energy has been funneled into work on three classes of compounds: pheromones, which influence the behavior or physiological development of members of the same species (for example, in mating or aggregating); allomones, which act on members of a different species to the advantage of the producer (for example,
defensive toxins, such as the bombardier’s spray); and kairomones, which affect members of a different species to the advantage of the receiver (for example, those monoterpenic pine resins that inadvertently attract parasites or predators to a wound).

The explanatory power of chemical ecology is unquestioned. Its descriptions of the intricacies of insect life are quite amazing. Nonetheless, David Dunn tells me, it has done little to slow the advance of bark beetles through the northern forests. Its primary pest-control tools—pheromone traps (which decoy the beetles or disrupt their behavior) and pesticides—have proven ineffectual or impractical. Despite hundreds of research papers and untold millions of dollars in research funds, the beetles march on.

Listen. They’re coming through loud and clear. Those squeaky chirps are the piñon engraver beetles. The female has a small, hard comb (the
pars stridens
) on the back of her head, which she grates against a scraper (the plectrum) located under the front edge of her prothorax. The male makes sounds too, but no one is sure how.

The range of sound-making organs in bark beetles is substantial. And so are the uses to which all the noise is put. Think of the Scolytidae as social insects. Not in the same way as eusocial insects, like the honeybees, with their elaborate nests and sharp divisions of labor. Social in a looser sense: they live in groups; they coordinate mass arrivals on target trees; they arrange spacing to ensure that they don’t settle too densely; some occupy their nests collectively. Such complex cooperative behavior presumes communication.

Research on bark beetle interaction has focused largely on chemical signaling; sound has been regarded as ancillary.
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Symptomatically, there is still nothing published on how bark beetles hear or what kinds of auditory organs they possess.
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But what if—as Dunn and Crutchfield propose—bark beetles are attracted to vulnerable trees not only by the aggregation pheromones of the male pioneers and the kairomones released in the wounded trees’
resin but also by bioacoustic cues, such as the internal explosions of gas bubbles during cavitation events? Could we provisionally assume that, like many butterflies, moths, mantises, crickets, grasshoppers, flies, and Neuroptera, bark beetles, too, may have hearing in the ultrasonic range? The rich ultrasonic sound-world of the piñon pine suggests as much, as do recent studies indicating that hearing among insects is far more widespread than previously assumed.
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Indeed, after spending time inside the piñon alongside the animals and scaled to their world, it becomes more and more inconceivable that so little research is being done on beetle bioacoustics and that the intensely interactive sounds inside the tree are arbitrary. Reviewing the piñon soundscape, Dunn and Crutchfield discover that “a very diverse range of sound signaling persists well after the putatively associated behaviors—host selection, coordination of attack, courtship, territorial competition, and nuptial chamber excavations—have all taken place. In fully colonized trees,” they write, “the stridulations, chirps, and clicks can go on continuously for days and weeks, long after most of these other behaviors will have apparently run their course.” What does this mean? Their inference is careful but important: “These observations suggest that these insects have a more sophisticated social organization than previously suspected—one that requires ongoing communication through sound and substrate vibration.”
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Recent research by Reginald Cocroft and his associates at the University of Missouri at Columbia raises yet another question. Cocroft has shown that the low-frequency and ultrasonic airborne sounds recorded by David Dunn are actually only one element of an insect’s sound-world. In huge numbers, it seems, insects that live on plants also communicate by the nonacoustic vibration of their living substrate. “Vibration-sensitive species,” write Cocroft and Rafael Rodríguez, “can not only monitor vibrations to detect predators or prey but also introduce vibrations into structures to communicate with other individuals.” By vibrating the leaves, stems, and roots of plants, insects send meaningful signals across significant distances (up to twenty-six feet in the case of stoneflies). Unconstrained by the physical limitations of airborne communication, they can deter predators by producing low-frequency signals that mimic far larger animals. Some, such as leaf-cutter ants,
vibrate to call their comrades to a high-quality food source. Others, such as larval tortoiseshell beetles, exchange vibrational signals that coordinate the formation of defensive groups. Still others, including thornbug leafhoppers, generate collective distress signals to summon their mothers when they are under threat. And needless to say, predators eavesdrop on vibrations to locate their prey (a practice that accounts for “vibrocrypticity,” by which some insects “move so slowly and generate so little vibration in the substrate that they can walk past a spider without eliciting an attack”). The diversity of vibrational signalers and signals is “fantastic.”
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Let’s reimagine the landscape of the soundscape. Let’s begin with all that busy, noisy, musical energy and open our senses wider still. And let’s assume not only multimodality but cross-modality—that, like our own, these senses make sense in combination rather than isolation.

Yes, the world of insects is a noisy world, a constant whir of acoustics: drumming, clicking, squeaking, chirping.

Yes, it’s also a vibrating world, so sensitive that even gentle winds can disrupt it and a rainstorm can cause it all to dry up or be drowned out.

Yes, it’s a chemical world, too: a nonstop, impossibly complex, wildly inventive molecular maze of attractants, repellents, potions, poisons, and disguises.

And yes, as we know from von Frisch’s honeybees, it’s a world of direct physical intimacies—touching, palpating, and substance sharing—and a world of visual cues, too.

It’s an intensely interactive world, a landscape across which animals of the same and different species connect and communicate.