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.