They're as small as a fingernail, but the damage that zebra mussels can cause belies their tiny size. That's why the feds are concerned that the invasive, quickly multiplying mollusks have been popping up in pet stores across the US, specifically in ornamental moss balls used as decor in aquariums, per Smithsonian Magazine. The first sighting was at the end of February in a Seattle Petco, the AP reports. After hearing about that report, a US Geological Survey staffer visited a pet shop in Gainesville, Fla., and found a zebra mussel in a moss ball there, per a USGS release. Since then, similar reports have come in from at least 19 other states, from the West Coast to the East Coast and as far north as Alaska (complete list here), as well as from British Columbia. The freshwater mussels can harm "native fish plants and other aquatic life ... clog pipelines used for water filtration, render beaches unusable, and damage boats," per the US Fish and Wildlife Service.
"This is one of the most alarming things I've been involved with in over a decade of working with invasive species," Justin Bush, executive coordinator for the Washington Invasive Species Council, tells KING 5. He adds that if the mussels, originally from Eurasia, find a foothold in his state, it could cost millions of dollars a year to keep them under control in Washington alone. So what should you do if you've decked out your own aquarium with moss balls? Assume the worst—that they're housing zebra mussels—and get rid of them, a USGS fisheries biologist tells the Detroit News. And it has to be done properly, meaning you have to destroy the mussels (the FWS offers tips on how to do so, including freezing, boiling, or bleaching the moss ball); place the moss ball in a sealed plastic bag and put it in the trash; and then drain the aquarium and thoroughly clean it. (Read more invasive species stories.)