D:        Today on "A Moment of Science," being an invasive species is hard on invaders...

Y:        [INTERRUPTING] Wait -- don't you mean that invasive species are hard on native species or environments?

D:        That is usually true as well; many studies have investigated the negative impact that invasive species have on natural ecosystems. But a study of invasive cane toads in Australia focused on challenges faced by invaders.

            Cane toads are large poisonous toads from South America. They were introduced into Australia in the 1930's with the hope that they would eat the cane beetles that were destroying sugar cane crops.   Unfortunately the toads didn't eat the beetles, but did eat almost every other small animal or insect in their path. The voracious toads are a double threat to the Australian ecosystem, because the toads are so poisonous that many Australian predators, including pets, have died from eating them.

Y:        Hmm, it doesn't sound like the invaders are having a hard time!?

D:        Well, the cane toads' success is due, in part, to how fast they migrate. A toad may move a half mile each night looking for new food and breeding opportunities. Since the fastest toads are the most successful, natural selection has resulted in larger toads with longer legs with each generation.  But speed has costs too. The researchers discovered that some of the largest toads develop severe spinal arthritis, and are more susceptible to infections than smaller, slower individuals.

Y:        That's interesting - but who cares if they get sick and arthritic? Aren't biologists trying to eradicate them in the first place?

D:        Scientists hope that by understanding the impacts that invasion has on the invading species, they might discover new ways to stop invaders in their tracks.