Spiney Water Flea

Common Name:  Spiny Water Flea
Scientific Name: Bythotrephes longimanus

Spiny water fleas are tiny crustaceans that are native to Europe and Asia. They were first found in Lake Huron in 1984 – probably imported in the ballast water of a trans-oceanic freighter. Since then, populations have exploded and the animal can now be found throughout the Great Lakes and in some inland lakes.  Likely means of spread for include the eggs and adults wind up unseen in bilge water, bait buckets, and live wells. Also, fishing lines and down riggers will often be coated with both eggs and adults. 

Identification
Adults range from 1/4 to 5/8 inch long. Spiny water fleas have a single long tail. On a fishing line, spiny water fleas look like bristly gobs of jelly with black spots. 

Spiny Water Flea, Photo: USGS.gov

Impacts
Spiny water fleas eat small animals (zooplankton), including Daphnia, which are an important food for larval and juvenile native fishes. In some lakes, they cause the decline or elimination of some species of native zooplankton. Fish do no feed on water fleas because their sharp spine makes them extremely hard to swallow. They become entangled on fishing lines and can clog the eyelets of fishing rods. 

Spiny Water Flea Photo © DFWI & J. Gunderson, MN Sea Grant

Help prevent the spread of this invasive species
Prevention is key to keeping spiny water fleas from spreading. Please ensure that you thoroughly clean and dry your fishing equipment and boat in between each use. 

If you find this animal in Northern Michigan, please contact Tip of the Mitt Watershed Council at (231) 347-1181 or email [email protected]. Our Watershed Protection team and Aquatic Invasive Species Patrol rely on caring citizens like you to help locate these aquatic invaders. If possible take a photo and record your exact location.