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Texas Invasive Species Institute

Texas Invasive Species Institute

Hammerhead flatworm/ Hammerhead slug

Bipalium kewense

Class: Turbellaria
Order: Tricladida
Family: Geoplanidae

Bipalium kewense

Photographer: C. Neff Source: TISI Citizen Report


The common name for this pest is very accurate as the head is shaped like a hammerhead shark, but rounded. Bipalium kewense is a terrestrial flatworm with a half-moon shaped head. It is typically light/honey colored, with 1 to 5 dark dorsal stripes (median stripes are thin), and a dark collar that is incomplete in this species (complete dark collar could be B. vagum). The body is "snake-like" being up to 15 inches long (usually 8-12 inches) and very narrow.

Ecological Threat

Known predator of earthworms that are necessary for the health of our forests, crops, gardens and compost piles. Bipalium species secrete chemicals through their skin to make themselves noxious to predators, and aid in the digestion of earthworms. These chemicals can cause skin irritation on humans if they hold the flatworm, and domestic mammals if they consume the flatworm. Furthermore, many flatworms can carry parasitic nematodes within them. All of these reasons are why we encourage safe practices and disposal.


Like all Bipalium, that have been studied, the hammerhead flatworm is hermaphroditic.  However, sexual reproduction has not been observed. Egg cases have been found. At least in temperate regions, reproduction seems to be primarily achieved through fragmentation: a small rear portion of the worm will pinch off, and "stay behind" as the worm moves forward. Within about 10 days, the head begins to form. This may happen a few times a month. If you see one, be sure to dispose of the whole creature.


Apparently brought to the U.S. with horticultural plants; it has been regularly found in greenhouses since 1901 (Esser 1981). They were reported as being so plentiful in New Orleans that they were used as demonstration material in zoology classes (Dundee and Dundee 1963).

Native Origin

Southeast Asia- Vietnam

Current Location

U.S. Habitat:  Prefers hot, humid environments, so it does well in greenhouses; in tropical and subtropical areas it can spread from greenhouses and is a "hitchhiker" in the landscaping, mulch, nursery industries.  During the day hammerhead flatworms spend their time under leaf litter, rocks and logs and such, and under shrubs, out of the sun; under dripping garden faucets. After heavy rains, they may be found out on the soil, driveways, patios, and  sidewalks.

Natural habitats: AL, CA, FL, GA, LA, MS, NC, SC, TX. (Possible temporary populations: AZ, MA, NH) 

Greenhouses: AL, CA, GA, IL, KY, MA, MI, NC, NJ, NY, OH, OK, SC, TN

TEXAS: Historical evidence reports this flatworm around the Beaumont area in the 1980s- however, consistent data is limited. Reporting and engagement from citizens like you is allowing us to understand the distribution.


No native species. There are other invasive Bipalium hammerhead flatworms appearing in Texas including Bipalium vagum from the Houston area, and it poses the same threats.


B. kewense can be killed with orange essence (citrus oil), and salt (as with slugs and snails). They can also be sprayed with a combination of citrus oil and vinegar; or just vinegar alone and it must be applied directly on the flatworm. Placing them in a Ziploc bag with salt or vinegar ensures the flatworm does not crawl away after treatment; then dispose of the sealed bag. Continuous removal of these invasive flatworms is necessary for the protection of naturalized earthworm populations.

 ** When handling live flatworms please use gloves, paper towel or a stick, and hands should be washed in warm soapy water, and rinsed in alcohol or a standard hand disinfectant.**


Esser, R. P. 1981. Land Planarians (Tricladida: Terricola). Contribution no. 227, Bureau of Nematology, Florida Department of Agricultural and Consumer Services, Division of Plant Industry, Gainesville, Fl. 

Ducey, P. K., Cerqua, J., West, L. J., and Warner, M. 2006. Eberle, Mark E., ed. Rare egg capsule production in the invasive terrestrial planarian Bipalium kewenseThe Southwestern Naturalist 51 (2): 252. doi:10.1894/0038-4909(2006)51[252:RECPIT]2.0.CO;2 

Dundee DS, Dundee HA. 1963. Observations on the land planarian Bipalium kewense Moseley in the Gulf Coast. Systematic Zoology 12: 36-37. 

Winsor, L. 1983. A revision of the cosmopolitan land planarian Bipalium kewense Moseley, 1878 (Turbellaria: Tricladida: Terricola). Zool. J. of the Linnean Soc. 79: 61-100.

Internet Sources

http://davesgarden.com/guides/bf/go/1839/#b. (Scroll down to Dixxie’s entry.) [Accessed Dec 8 2014] 

http://davesgarden.com/guides/bf/go/1839/#b. [Accessed Dec 8 2014] 

http://entnemdept.ufl.edu/creatures/misc/land_planarians.htm. [Accessed Dec 8 2014]

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