Fear Powers Zombie Bugs
Work with glued spiders and stressed grasshoppers shows how fear can transform an ecosystem even after death.
File under “Career change.” While the rest of us mopes suffer the nine-to-five in our stuffy cubicles, ecologist Dror Hawlena spends his days picking through lizard poop, gluing spiders’ mouths shut, and dissecting grasshopper guts under a microscope. He’s tracked leopards, ibexes, and wild boars. When field trips takes him out of the office, they take him waaay out of the office, to the Yale-Myers forest, the Negev Desert, Glacier National Park, the Balearic Islands, and the Wadi Rum valley, in Connecticut, Israel, Montana, Spain, and Jordan, respectively. His coworkers are guys like Acanthodactylus beershebensis and Podarcis lilfordi.
Hawlena’s research focuses on how reptiles and insects manage risk and respond to stress. He studies why lizards’ rainbowed tails lose their color (working theory: as they grow up and hunt less, they need fewer mechanisms to distract predators) and how grasshoppers become super-athletes when preyed upon by spiders.
For this last inquiry, two years ago, he raised several dozen grasshoppers in outdoor plots and then introduced spiders to half the cages, so that the hoppers either lived worry-free or in constant fear of being eaten. To prevent any casualties—Hawlena couldn’t study the athleticism of a bunch of dead grasshoppers—he carefully glued the spiders’ mouths shut with rubber cement before turning them loose in the plots. The at-risk grasshoppers—which weren’t taking any chances, rubber cement or no—quickly learned new defensive behaviors. When Hawlena staged a mini insect Olympics some months later, the congenitally stressed grasshoppers could jump faster, father, and higher than their worry-free friends.
The march of science beats steadily on. Hawlena’s newest research, which appeared in June in Science, involves more unhappy grasshoppers and sticky-mouthed spiders. In a series of three experiments, Hawlena, formerly a postdoctoral researcher at the Yale School of Forestry and now a senior lecturer at the Hebrew University of Jerusalem, and his colleagues at Yale demonstrated that stressed insects have a pronounced impact on their ecosystems—even after their deaths.
From previous work, the ecologists knew that stressed grasshoppers underwent physiological changes in response to environmental threats. At-risk hoppers have elevated metabolisms and must devote the bulk of their calories to surviving, rather than growing or reproducing; as a result, they eat less protein and more carbohydrates, which provide bursts of quick energy. This alters what ecologists call their “carbon-to-nitrogen” ratio. The body of a preyed-upon grasshopper contains a higher proportion of carbon to nitrogen, both because of its carb-intensive diet and because stress hormones cause the hopper to convert its body proteins into glucose, excreting nitrogen in the process.
The researchers discovered that this small change in grasshopper physiology—more carbon, less nitrogen—dramatically slowed the rate of decomposition in the meadows where they lived and died. After their bodies had broken down and returned to the soil, the microbial communities underfoot had a harder time processing leaf litter that fell to the ground. Hawlena theorizes that this is because nitrogen performs a critical part in decomposition processes—it primes the microorganisms that break down animal biomass (i.e. insect bodies) and plant organic matter (i.e. leaf litter) and return their minerals to the soil and air. In the test plots where the bodies of stressed, nitrogen-poor grasshoppers fell, less of the key element was available, creating a negative feedback loop: less nitrogen meant biomass was slower to decompose, shortchanging the soil microbes of even more nitrogen, ad infinitum. The consequences didn’t just ripple through the ecosystem—they amplified, too.
Hawlena and his colleagues were surprised by the finding, he told me from his office in Jerusalem. “We double and triple checked every result because it was too good to be true.” Conventional wisdom held that, given the sheer amount of vegetation growing, dying, and decomposing in the meadow, a few grasshopper bodies would be too small to have any effect on the cycle. As the authors note, the hoppers weighed 140 times less than the leaf litter added on top of them—yet they slowed its decomposition threefold. A little stress goes a long way.
Oh, and about those glued spiders … As a grown man still scarred by a childhood viewing of “Arachnophobia,” I wanted the full details. “You take the spider and, in order not to crush it, you hold it with a very soft sponge,” Hawlena explained. “Then you walk under the microscope and with a very delicate pin you just add the cement to the mouth spot. You put it close and the spider actually tries to bite it. It’s just a tiny blob.”
Apparently not everyone finds this image so delicious. Hawlena made the mistake of perusing readers’ comments on news stories that appeared in recent weeks, after the publication of the Science study. “A few of them were extremely upset with the methodology. I will not repeat the words that they used to describe me, but definitely not nice ones. Big time.”