Texas Invasive Species Institute

Texas Invasive Species Institute

Spiny Water flea

Bythotrephes longimanus

Class: Branchiopoda
Order: Diplostraca
Family: Cercopagidae

Bythotrephes longimanus

Image:New York Invasive Species Clearinghouse Affiliation: Cornell University Cooperative Extension Source:www.EOL.org Copyright:CC BY-NC


Bythotrephes longimanus is a planktonic crustacean less than 0.6 inches long and has a long and straight tail spine that is twice as long as the body. Many characteristics are hard to identify without magnification because they gather in gelatinous clumps (pictured right). What can be seen is the head is clearly separated from the trunk and has a single large black compound eye. Two swimming antennae are used to propel the animal through the water and are attached just behind the head. The spine bears 1-4 pairs of barbs depending on the animal’s age. They have four pairs of legs with the first pair, being the longest pair, is used for catching prey while the others are used to grasp the prey while eating.

Ecological Threat

At first this crustacean was just a nuisance to fisherman but now it has been documented to change ecosystem structure. After the spiny water flea is established, the community structure of the zooplankton alters and there’s a reduction in herbivore crustaceans like Daphnia and rotifers. In consuming those invertebrates, spiny water fleas also compete for food with the plankton-feeding larvae of several fish species as well as the native giant water flea (Leptodora kinrtii); making Bythotrephes longimanus a threat on several levels.


Bythotrephes longimanus can reproduce with both sexes and parthenogenically (all females). Most of the time females reproduce by parthenogenesis and produce 1-10 eggs that develop into new females without fertilization by males. A new generation may be produced every two weeks in the summer. The sex of the young is determined not by genetics, but by the environment. When conditions deteriorate in the fall, males start being produced. They mate with the females and produce “resting eggs”; that are carried in the brood pouch and then are released to settle on the bottom of the lake, where they go into a “resting phase” through the winter and hatch into females. The brief sexually reproducing part is to promote genetic diversity.


Bythotrephes longimanus was discovered in 1984 in Lake Huron, supposedly via onboard freighters from Russia. By the next year they were found in Lakes Erie and Ontario and by 1986 they were found in Lakes Michigan and Superior. By early 2002, they had been reported from 66 lakes in the northern United States and southern Canada. In 2007, they were found in Wisconsin and in 2008 they were found in New York’s Adirondack Mountains.

Native Origin

Native Origin: Unsure but thought to be around Northern Europe and Asia

Current Location

U.S. Habitat: Estuaries, lakes, wetlands and even brackish waters; limited to water temperatures between 39-86oF and salinity of 0.04-8.0%.

U.S. Present: IL, IN, MI, NY, OH, PA, WI,  


Once the spiny water flea is established it is nearly impossible to eliminate but education and prevention are crucial to keep this crustacean only in the Great Lakes. Educational campaigns encourage fisherman to clean gear properly and empty bilges, live-wells and bait buckets responsibly before moving to another lake.


Text References

Branstrator, D. K. 2005. Contrasting life histories of the predatory cladocerans Leptodora kindtii and Bythotrephes longimanus. Journal of plankton research, 27(6):569-585.

Branstrator, D. K., Brown, M. E., Shannon, L. J., Thabes, M., & Heimgartner, K. 2006. Range expansion of Bythotrephes longimanus in North America: evaluating habitat characteristics in the spread of an exotic zooplankter. Biological Invasions, 8(6):1367-1379.

Johnson, P. T., Olden, J. D., & Vander Zanden, M. J. 2008. Dam invaders: impoundments facilitate biological invasions into freshwaters. Frontiers in Ecology and the Environment, 6(7):357-363.

Woodward, Susan L., and Joyce Ann. Quinn. 2011. Spiny Water Flea. Encyclopedia of Invasive Species: From Africanized Honey Bees to Zebra Mussels. Santa Barbara, CA: Greenwood. 95-98. Print.

Yan, N. D., Girard, R., & Boudreau, S. 2002. An introduced invertebrate predator (Bythotrephes) reduces zooplankton species richness. Ecology Letters, 5(4):481-485.

Internet Sources






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