Spiny Water Flea

Bythotrephes longimanus

Invader Images

    • View of a spiny waterflea under a microscope
      View of a spiny waterflea under a microscope
    • Spiny waterfleas caught on fishing tackle
      Spiny waterfleas caught on fishing tackle


Spiny water flea grows to about 12 mm when fully mature. The long, spiny tail makes up roughly 70% of this species' total length, and has between one and four pairs of barbs. Also, spiny waterflea have four pairs of legs on the underside of their body. Similar in appearance to the fishhook water flea, but lacking the “hook” at the end of its tail. Spiny waterflea can often be seen by the naked eye, and will readily accumulate in a blob-like structure on fishing line and other tackle that is dragged through the water.



Northern Europe and Asia.


Spiny waterflea prefer cold, and open (generally pelagic) waters, but can persist in a wide range of lentic conditions.


Spiny water flea populations tend to peak between early September and early November. When food (other zooplankton) is readily available and temperatures are warm, males will feed while females reproduce through parthenogenesis, not requiring fertilization from their male counterparts. During this time, only females are produced (sex of offspring is environmentally controlled by temperature and prey availability). As water cools and food declines, more males will be produced. Females can produce between 1-24 embryos which can be found in their brood pouch—if successful, these embryos can be dropped into sediment as resting eggs where they often survive the winter, and have a chance of being transported in mud. Eggs will hatch in spring/early summer.

Ecological Threat

Lake monitoring has shown the spiny water flea, as a result of predatory behavior, to reduce species richness and population sizes within zooplankton communities. This has large implications for Lake Champlain (and other Vermont water bodies acting as fisheries) as it could significantly alter aquatic food web dynamics through direct competition with small fish for zooplankton. Reduction in water clarity (remedied by phosphorous loading reduction, an expensive process) is a notable effect of spiny water flea, one with serious monetary implications. This reduction is water clarity is attributed to spiny water flea due to the fact that it so voraciously predates other algae grazers.

Management Options

Legal Status

No current legislation regarding the transport of spiny water flea exists in Vermont.

Control Options & Examples

Current management efforts surrounding spiny water flea are focused on spread prevention. Decontamination of boats, fishing gear, and outerwear exposed to infested water sources is crucial to stopping this species spread. Draining water from motors, live wells, and bilges is another practice that can reduce the threat this species poses to uninvaded Vermont water bodies.


Vermont Distribution

Spiny waterflea was first documented in Lake Champlain in 2014, where the only known population in Vermont exists. They are also found in the Great Lakes and many locations in the northern Midwest and southern Canada.

U.S. map of Spiny waterflea distribution

How You Can Help

For most aquatic invasive species, humans are the primary vector of transport from one waterbody to another. Many of these nuisance plants and animals can be unknowingly carried on fishing gear, boating equipment, or in very small amounts of water in a watercraft. The easiest and most effective means to ensure that you are not moving aquatic invasives is to make sure that your vessel, as well as all your gear, is drainedclean, and dry.


  • CLEAN off any mud, plants, and animals from boat, trailer, motor and other equipment. Discard removed material in a trash receptacle or on high, dry ground where there is no danger of them washing into any water body.

  • DRAIN all water from boat, boat engine, and other equipment away from the water.

  • DRY anything that comes into contact with the water.  Drying boat, trailer, and equipment in the sun for at least five days is recommended. If this is not possible, then rinse your boat, trailer parts, and other equipment with hot, high-pressure water.

Interested in monitoring for aquatic invasives?


Berg, D.J., and D.W. Garton. 1988. Seasonal abundance of the exotic predatory cladoceran, Bythotrephes cederstroemi, in western Lake Erie.  Journal of Great Lakes Research 14(4):479-488.

Liebig, J., A. Benson, J. Larson, T.H. Makled and A. Fusaro. 2016. Bythotrephes longimanus. USGS Nonindigenous Aquatic Species Database, Gainesville, FL.  Revision Date: 6/4/2013 

Walsh, J.R., S.R Carpenter, and M.J.V. Zanden. 2016. Invasive species triggers a massive loss of ecosystem services through a trophic cascade. Proceedings of the National Academy of Science 113(15):4081-4085.

Yan, N.D., R. Girard, and S. Boudreau. 2002. An introduced invertebrate predator (Bythotrephes) reduces zooplankton species richness.

U.S. Environmental Protection Agency (USEPA). 2008. Predicting future introductions of nonindigenous species to the Great Lakes. National Center for Environmental Assessment, Washington, DC; EPA/600/R-08/066F. Available from the National Technical Information Service, Springfield, VA, and http://www.epa.gov/ncea.


USGS Nonindigenous Aquatic Species, Spiny Water Flea

Aquatic Invaders, Sea Grant, Spiny Water Flea