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Bipalium is a genus of large predatory land flatworms, terrestrial planarians. They are often loosely called "hammerhead worms" or "broadhead planarians" because of the distinctive shape of their head region. Land planarians are unique in that they possess a "creeping sole" on their ventral side. Several species are considered as invasive to the United States and to Europe. Some studies have begun the investigation of the evolutionary ecology of these invasive planarians.
Bipalium species are predatory. Some species prey on earthworms, while others feed on mollusks. It has been shown that the flatworms can track their prey. When captured, earthworms will begin to react to the attack, but a flatworm uses the muscles in its body as well as sticky secretions to attach itself to the earthworm to prevent escape. Several studies have indicated that the planarians will cover, or cap the prostomium, peristomium and anterior end to end the violent reaction by the earthworm. To feed on its prey, a flatworm extends its pharynx out from its mouth on the mid-ventral portion of its body and secretes enzymes that begin digestion of the earthworm external to the flatworm. The liquefied earthworm tissues are sucked into the branching gut of the flatworm by ciliary action.
Reproduction in Bipalium may be asexual or sexual and all species are hermaphroditic. B. adventitium reproduces sexually and creates egg capsules, which hatch around 3 weeks post-deposition. The egg capsules have a tough exterior and generally contain multiple juveniles. B. kewense have rarely been observed using egg capsules as a primary method of reproduction. Asexual fragmentation is the main reproductive strategy in B. kewense in temperate regions. Juveniles of this species, unlike B. adventitium, do not appear the same coloration as parents in their early days.
There is very little known about the ecology of terrestrial planarians, however research has been done on different genera and species, including several native and invasive species in Brazil, Arthurdendyus triangulatus, Rhynchodemus  and Bipalium. Currently, there are four known invasive species to the United States: B. adventitium, B. kewense, B. pennsylvanicum and B. vagum. It is believed that these planarians came to the US on horticultural plants.
Bipalium kewense has been found commonly in American greenhouses since 1901. Planaria are voracious predators of earthworms, and Bipalium kewense and Dolichoplana Striata Moseley have been identified as nuisances in the southern USA in earthworm-rearing beds. Control of the species is difficult due to the lack of predators. As noted by the University of Florida IFAS department,
Other animals rarely devour land planarians, since surface secretions appear distasteful, if not toxic. Protozoans, including flagellates, ciliates, sporozoans, and nematodes have been detected in land planarians. Because of their cannibalistic habit, land planarians may be their own worst enemy.
Individual Bipalium adventitium are characterized by a single dark dorsal stripe. They were first discovered in the US in California and New York but have been found in Illinois as well as most northern states Bipalium kewense have five dark dorsal stripes and a partial dark collar. They have undergone several name changes since their discovery in North America. B. kewense is commonly found across the southern regions of the US. B. kewense is found worldwide in tropical and subtropical regions. Bipalium pennsylvanicum is characterized by its dark brown head and three dorsal stripes. Thus far it has only been found in Pennsylvania and in coastal South Carolina in 2014. Bipalium vagum is characterized by two dark dorsal blotches on the head, a thick black band around the neck and three dark dorsal stripes. This species has recently been found in several Gulf Coast states.
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