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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: S. E. Thorpe Source: Wikimedia Commons

Description

A terrestrial flatworm with a half-moon shaped head, hence its name (think hammerhead shark with a rounded head).  Typically light colored, and photos (Google images) indicate that it has 1 to 5 dark dorsal stripes and a dark collar that may be complete (if there are three or more stripes, it appears that the median strip is thin).  Up to 30 cm long, 0.2-0.5 cm wide.

Ecological Threat

Known predator of earthworms, but as it is not well-studied, it may feed on other organisms.  Community effects unknown.  Land planaria have been found in caves (although it isn’t clear whether this is true for this particular species), so it is possible that they may impact cave ecosystems (such as found in Texas). 

Biology

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. 

Some sources say that a relative, B. adventitious has toxic (or at least noxious) skin secretions that make it noxious to predators, but one source fed a B. kewense to a salamander/newt (Dixxie 2014 in Internet Brands 2014): “I went outside turned over a couple stones and found a 4" salamander, I pulled it out of the cup it was in, dropped it in front of the salamander; goodbye planarian bipalian or whatever it was. I live on 20 acres, mostly woods and have thousands of newts and salamanders, guess that's why I’ve never seen one.”

History

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

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. 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. They may be found out on the soil, driveways, patios, sidewalks after heavy rains. Feed and move about during the night.

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

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

Resembles

None

Management

Reports indicate that individual B. kewense can be killed with orange essence, and (as with slugs and snails) salt.

References

Contributions from Texas Invasives for this species page are greatly appreciated.

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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