Massive grasshoppers called wetas once hopped throughout New Zealand. Now threatened or endangered in most of that country, their scarcity could spell trouble for some of their food sources. Researchers have found that these omnivorous insects sometimes munch on fruits, passing seeds through their guts unharmed. This behavior is essential to the well-being of plants, as the journey through the gut seems to be a rite of passage necessary for some seeds to germinate, says Kevin Burns, an ecologist at Victoria University of Wellington, New Zealand.
Insects are not known for eating fruits and dispersing undigested seeds. But because New Zealand originally lacked rats, which can spread seeds, Burns and his Victoria University colleagues Catherine Duthie, a graduate student, and George Gibbs wondered if the mouse-sized wetas had taken over the seed-dispersal job often held by these furry species. That role would make sense, as wetas are known as "invertebrate mice" because of their size and nocturnal habitats, Burns points out.
In the lab, the wetas chowed down on all 19 kinds of fleshy fruits tested. The seeds of five--including the tree and creeping fuchsias, and snowberry--passed through the gut intact, the researchers report in the 17 March issue of Science. In field tests, the researchers found that 64% of the weta scat collected had seeds or seed fragments. Wetas passed only small seeds intact, as larger ones were damaged by chewing or were too big to eat at all. Those pooped-out seeds sprouted--and in general, were more likely to grow than were seeds the researchers removed from the fruits and planted. Burns suggests mouth or gut activity may have roughed up seed coats, which encourages certain seeds to germinate.
Typically, seeds spread by animals--including insects--simply stick to the outside of the body and eventually fall off, says Kevina Vulinec, a wildlife ecologist at Delaware State University in Dover. "The paper highlights a new discovery about intact ingestion and subsequent dispersal of seeds by insects," she says. That discovery alone is surprising, she notes. "But even more striking is this insect filling the niche of small mammals."