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Toad-Munching Spider Poses Rising Threat

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American toads and wolf spiders don't play well together - the spiders are swift predators, capable of catching and eating young amphibians.

Normally, other spiders keep the wolf spider population in check. But the abundance of an invasive plant, Japanese stiltgrass, gives wolf spiders enough cover to escape would-be hunters.

Japanese stiltgrass is "kind of like a tall shag carpet," says John Maerz, a professor at the University of Georgia, in a statement. Spiders can disappear into the tall grass, and then lie in wait to prey on unsuspecting toads.

Maerz and his colleagues recently found a link between areas of high spider density and low toad survival, the biologists report in the journal Ecology. Where stiltgrass covered the forest floor, wolf spider populations increased 33 percent and toads were 65 percent less likely to survive. "In other words, the grass is degrading the best forests for young toad survival," says Maerz.

(Jayna DeVore/UGA)

Untangling all the effects an invasive species has on an ecosystem, and tracking where invading organisms end up, is notoriously difficult. Voracious lionfish, long known to be threats to native fish species in the Atlantic ocean, have recently been found to tolerate freshwater, opening up new areas to the spiny predators.

It's possible the impact of an increased wolf spider population, likewise, has rippled out to more species. "Spiders are actually tremendously important and incredibly abundant predators on the forest floor," Maerz says, "and they will eat many of the small species that live there, so this effect is unlikely to only influence toads."

Japanese stiltgrass, which likely traveled from Asia to the United States as packing material, can transfer between forests via seeds stuck to hiking boots. To prevent the aggressive grass from spreading, conservation group the Nature Conservancy advises that people avoid treading through the tall silvery-striped plants, and brush off boots after suspected contact.

(Dendroica cerulea/Flickr)