Carcasses of jumpy insects taint soil
Terrified insects can haunt their homeland after they die. Chemical remnants of fear in the rotting corpses of grasshoppers slow the decomposition of dead grass and other debris important for fertilizing new plant growth, a new study finds.
Spiders that frighten grasshoppers may thus play an unrecognized role in shaping ecosystems, adding a menacing presence that both cows the predators’ prey and suppresses the local vegetation, researchers report in the June 15 Science.
A team working at Yale spooked Melanoplus femurrubrum grasshoppers by raising them in cages with Pisaurina mira spiders. The arachnids’ mouth parts had been glued shut, so they could scare but not kill the hapless insects. Stress boosts a grasshopper’s metabolism and appetite for carbon-rich carbohydrates. So compared with insects living in predator-free cages, grasshoppers cohabitating with eight-legged horrors were made of more carbon and less nitrogen.
That change in composition proved to be problematic for soil microbes, which need nitrogen to break down plant litter. When the researchers added the carcasses of once-fearful grasshoppers to dirt, microbial activity dropped by 62 percent in the lab and 19 percent in plots of land outdoors.
D. Hawlena et al. Fear of predation slows plant-litter decomposition. Science, Vol. 336, June 15, 2012, p. 1434. doi:10.1126/science.1219973.