Invasive Species

A Two for One Special

Moss balls and zebra mussels

Zebra mussels on a moss ball, surrounded by other moss balls and with “Shrimp Buddies” and “Betta Buddies” packaging in the background
Moss balls come in a variety of styles and sizes including Marimo Balls and Shrimp Buddies, but there’s more to these moss balls than meets the eye. 📷 Deborah Kornblut/USFWS
Two terrariums each with a single moss ball on a patio table surrounded by other house plants
USFWS Law Enforcement Officer holds two types of packaging for moss balls, one packaging being Shrimp Buddies and the other being Betta Buddy
These moss balls are unlike other moss in that they are a filamentous algae sourced primarily from eastern Europe. 📷 Deborah Kornblut/USFWS

A Kinder Surprise in the Moss Balls

Despite the appeal of a ball of filamentous algae in your home, moss balls can have a serious side-effect. Moss balls can carry zebra mussels — a tiny invasive species also from eastern Europe.

Size comparison between a zebra mussel, a push pin, and a moss ball with mussels as the smallest
Column of zebra mussels on a moss ball
Zebra mussels and other materials on a moss ball
Alaska was spared from this invasion, until March of 2021 when zebra mussels were first documented riding into the state on aquarium moss balls. 📷 Deborah Kornblut/USFWS
Zebra mussel on a transparent ruler which shows that the mussel is about one fourth inch long
Individual mussels tend to be quite small. While a zebra mussel can grow up to two inches long, most are less than an inch. 📷 Deborah Kornblut/USFWS
Shopping cart covered in zebra mussels
Up close view of a mussel covered in zebra mussels.
(Left) Shopping cart covered in invasive mussels. 📷 James F. Lubner/University of Wisconsin Sea Grant Institute (Right) Up close view of a mussel covered in zebra mussels. 📷 D. Jude/University of Michigan
Comparison between a zebra in the foreground of a mountain landscape with bears and a shell covered in zebra mussels in a riverbed with salmon
It might seem obvious that there is a big problem with the picture on the left, but what about the picture on the right? Photo composite by Sabrina Farmer/USFWS. 📷 Brown bears- Lisa Hupp/USFWS; Salmon- Kentaro Yasui; Zebra - Philip Bryden; Mussels- D. Jude/Univ. of Michigan
Holding a terrarium with a moss ball above a bathroom sink
Report moss balls, zebra mussels, or any other unexpected critters to ADF&G. 📷 Deborah Kornblut/USFWS

Stories from Alaska by the U.S. Fish & Wildlife Service