Spiny Waterflea

Bythotrephes longimanus

spiny waterflea title pic

The Spiny Waterflea (Bythotrephes longimanus) is crustaceous zooplankton of the suborder Cladocera. It is native to freshwater lakes in northern Europe and Asia. Both in their native range and throughout the regions in which they have been introduced, the spiny water flea prefers large, deep lakes whose benthic zones have relatively low summer temperatures. Nevertheless, they can also be found in shallower lakes, as well as rivers.

They were introduced into the Great Lakes by the discharge of ballast water from ocean-traveling ships and were first discovered in Lake Ontario in the early 1980s. Local dispersal methods of the spiny water flea include swimming between continuous bodies of water and being moved via anglers and recreational boaters to inland lakes.


Spiny water fleas prey upon smaller zooplankton—cladocerans, copepods, and rotifers—which are important food sources for juvenile native fish. And because of their ability to quickly reproduce, spiny water fleas are capable of dominating control over their food supply. This dominating capability has adverse effects on the growth and survival rates of the young fish in which spiny water fleas compete.

In addition to their effects on lake ecosystems, spiny water fleas are also well known for hooking themselves onto fishing lines in clumps consisting of hundreds of individuals, which can clog fishing lines to such an extent that they are unable to be reeled in and must be cut.

spiny waterflea on line


Habitat/Distribution: Spiny water flea prefers deep lakes, but can be found in shallow lakes and rivers. They can be found in gelatinous globs on fishing lines and downrigger cables. It is distributed in freshwater sources throughout the northeastern United States. It was found in Lake Huron in 1984, Lake Ontario and Lake Erie in 1985, Lake Michigan in 1986 and Lake Superior in 1987.




 The spiny water flea has a hard outer shell. The species’ most noticeable feature, however, is its long tail spine. The spine makes up 70% of its total body length and contains 1-4 pairs of thorn-like barbs. Their head consists primarily of a single, large eye and a pair of mandibles. The spiny water flea has four pairs of legs, the first pair being considerably longer than the others.

The spiny water flea shares its large tail spine characteristic with a confamilial (shared taxonomic family origin), the fishhook water flea (Cercopagis pengoi). To differentiate these two water fleas apart compare their body sizes and the terminal shape of their tail spines. The spiny water flea is much larger than its fishhook relative and possesses a more robust spine. Additionally, as its name suggests, the end of the fishhook water fleas tail spine has a fishhook shaped curve, which is not found on the spiny water flea. The spiny water flea can reach body lengths of up to 15 mm.

spiny waterflea identification 1

Control and Management

Physical Control: Clean all aquatic equipment with either high pressured (>250 psi) or hot (>122°F) water after each use in bodies of water containing spiny water flea as a part of regular equipment maintenance.

Use fishing lines designed specifically to prevent the spread of water fleas (ex. the Flea Flicker brand), which has been shown to significantly reduce the fouling of fishing lines by these organisms.

Biological Control: Although spiny water fleas are eaten by numerous species of fish—yellow perch, walleye, white bass, alewife, bloater chub, chinook salmon, emerald shiner, spottail shiner, rainbow smelt, lake herring, lake whitefish, and deepwater sculpin—their long, unique spines make them quite difficult to swallow when preyed upon by smaller individuals. So there are no known effective biological control methods at this time.

Photo Credits: 

Title photo: Northeast Aquatic Nuisance Species Panel. Habitat/Distribution map: United States Geological Survey. spiny water flea on fishing line:  Jeff gunderson, (images.dnr.state.mn.us). Fishhook vs spiny water flea photo: (www.protectyourwaters.net).


“Bythotrephes Longimanus (crustacean).” Global Invasive Species Database. Ed. Richard P. Barbiero. N.p., 10 Aug. 2005. Web. <http://www.issg.org/database/species/ecology.asp?si=151&fr=1&sts=sss&lang=EN>.

“Harmful Aquatic Hitchhikers: Crustaceans: Spiny Water Flea and Fishhook Water Flea.” Protect Your Waters. N.p., n.d. Web. <http://www.protectyourwaters.net/hitchhikers/crustaceans_spiny_water_flea.php>.

Liebig, J., A. Benson, J. Larson, T. H. Makled, and A. Fusaro. “Bythotrephes Longimanus.” NAS – Nonindigenous Aquatic Species. USGS, 4 June 2013. Web. <http://nas.er.usgs.gov/queries/factsheet.aspx?SpeciesID=162>.

“Prevent the Spread of Aquatic Invasive Species.” New York State Department of Environmental Conservation. N.p., n.d. Web. <http://www.dec.ny.gov/animals/48221.html>.

“Spiny Waterflea (Bythotrephes Longimanus).” Minnesota Department of Natural Resources. N.p., n.d. Web. <http://dnr.state.mn.us/invasives/aquaticanimals/spinywaterflea/index.html>.

“Spiny Waterflea (Bythotrephes Longimanus) – FactSheet.” USGS.gov. United States Geological Survey, 17 June 2015. Web. 03 Aug. 2015. <http://nas.er.usgs.gov/queries/factsheet.aspx?SpeciesID=162>.


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