Zebra mussel

Dreissena polymorpha · Aquatic life

Whole animal · Photo: CC0

InvasiveMollusk (mussel, clam, snail)

Also called Dreissena, Dreissenid mussels

State listing

Idaho: Prohibited invasive species
Oregon: Prohibited
Wyoming: Game and Fish aquatic invasive species

How to identify Zebra mussel

Small, D shaped mussel usually under 1 inch
Usually has zigzag or striped dark and light bands
Flat underside with a sharp ridge, so it sits upright on its side
Attaches to hard surfaces with tough threads (byssal threads)

Similar species

Quagga mussels are rounder and roll over when placed on their side. Native mussels and Asian clams do not attach with threads.

Profile

Season	Present all year; spawns in warm months.
Starts	Spawns as water warms past about 54 F
Depth	Shallow to moderate depths
How it spreads or reproduces	Microscopic larvae (veligers) in boat water and adults attached to boats, trailers and gear; also found in aquarium moss balls sold in pet stores in 2021
Habitat	Lakes, reservoirs, rivers and canals, on rocks, docks, pipes, plants and boats.

Why it matters in a lake

Not established in Idaho, Oregon or Wyoming, and states inspect boats to keep it that way. If established it would clog irrigation pipes, intakes and screens and change the food web; report any suspected find right away.