Since they were first released as live bait in the mid-twentieth century, rusty crayfish have roamed lake bottoms in northern Wisconsin, gobbling native fish eggs, destroying aquatic plants, and generally wreaking havoc on entire lake ecosystems. Today, in some lakes, traps can routinely pull up 50 to 100 rusty crayfish at a time, compared to two or three native species. But in other lakes nearby, populations seem to be declining. In a new study published in Ecology, scientists document the crash and explain what could be behind it.