They look like earthworms, but these invasive worms are devastating to Oregon's soil.In a small community plot at Salem’s Sunnyside Gardens in October, Kathy Arnold crouched beside her Swiss chard last October. She turned the soil with a gardening fork until she unearthed what she was looking for.“Here’s one,” Arnold said. “He’s very wiggly.”She picked up what looked like a typical earthworm. It began twitching and thrashing in her palm.“They’re…