Flatworm Fiesta

In 2014, a giant discovery was made regarding the terrestrial planarians Bipalium adventitium and B. kewense. Tetrodotoxin, a highly potent neurotoxin, was recorded in these species. 

This marked the first instance of tetrodotoxin in terrestrial invertebrates, underscoring the potential danger these species pose. Tetrodotoxin had previously been found in many marine organisms, including the Blue-ringed octopus, and is named after its initial discovery in pufferfish species, which belong to the order Tetraodontiformes. The name of this order is due to the form of the beak, which looks like 4 (tetra), teeth (odont): Formes means shape.

 

These worms, known as shovel-headed garden worms or hammerhead worms, are predators of other worm species, such as earthworms.

A Bipalium worm. Specific species are identified by their distinctive coloration, which often features colored bands and blotches. The one pictured here (stolen from thoughtco.com) has a very distinct head. However, the shape of the head varies among species.

Bipalium kewense has five dark dorsal stripes and a partial dark collar. Bipalium kewense, the New Guinea shovelheaded Flatworm, has undergone several changes in its taxonomic classification since it was first described. Bipalium kewense was originally described by Moseley in 1878. Over the years, it has been referred to by several synonyms, including Bipalium adventitium von Graff, 1899 and Placocephalus kewensis (Moseley, 1878). The currently accepted scientific name is Bipalium kewense.

 

Bipalium vagum has two dark dorsal blotches on the head, a thick black band around the neck, and three dark dorsal stripes. Bipalium vagum was first described by von Graff in 1899. Its common name is variable, so let’s choose one. The Wandering Hammerhead Flatworm is a name that sticks out to me. Bipalium vagum has been found in several Gulf Coast states, and in 2022, specimens were located further north in Arkansas. 

 

They are earthworm predators, feeding on many species of earthworm (there are hundreds of earthworm species in North America). Some known worm predators, like herpetofauna, don’t chow down on these beasts. There is no news on whether the early birds do. 

 

These planarians are non-native to the US. They may have dramatic effects on local worm populations, making them invasive. Earthworm rearing in the southern US may suffer.  Bipalium worms prefer warm and humid environments. They are sensitive to desiccation and temperature extremes, which can limit their distribution. This explains their common presence in greenhouses.

 

In the US, they were first discovered in California and New York but have been found in many states, including many northern states. In 2019, they were discovered in Montreal, Canada. B. kewense is commonly found across the southern regions of the US and worldwide in tropical and subtropical regions. Another species, Bipalium pennsylvanicum, is recognized by its dark brown head and three distinct dorsal stripes. It was found in Pennsylvania and coastal South Carolina in 2014.

 

Flatworms carrying toxins, coming soon to a place near you.

 

 

Ecology:

Originally native to Southeast Asia, many species appear to be invasive worldwide. Bipalium worms are typically found in moist terrestrial environments. They prefer humid conditions and are often found under rocks, leaf litter, and logs in gardens, forests, and greenhouses.

 

Like many flatworms, Bipalium worms have remarkable regenerative abilities. They can regenerate lost body parts, which aids in both survival and asexual reproduction. Bipalium worms can reproduce asexually through fragmentation. A small piece of the worm can regenerate into a complete individual.

 

Bipalium worms are carnivorous and use a unique hunting strategy, secreting sticky mucus to immobilize their prey before consuming it. They use their pharynx to secrete digestive enzymes onto their prey, which liquefies the prey's tissues. The flatworm then absorbs the nutrients. This eversion of the pharynx is similar to that done by nemertine worms, but I doubt it's as extensive (I could not find a hammerhead worm everting, so the video links to a Nematostella nemertine worm).

 

Nemertine worm everting:

https://youtu.be/xaBzFTOk-_g

 

 

 

Be wary, these flatworms could be dangerous:

PennState Extension has this to say: Paraphrased.

 

Management of land planaria in the landscape is nearly impossible, as many species are well established, and few control recommendations are available.

 

Individual flatworms can be killed by placing them in alcohol or freezing them in a bag. When handling flatworms, gloves should be worn, or the hands should be washed afterward. The risk from prolonged exposure to chemicals in land planaria mucous is likely low but unknown, so caution should be used. Salt can be applied to individual planaria to avoid touching them altogether. If salt is used, use caution when applying it around plants to prevent harming vegetation.

 

Do not cut up land planarias to control them. Terrestrial flatworms can regenerate from fragments. 

 

 

 

Resources and Further Reading:

 

Ducey PK, Noce S. 1998. Successful invasion of New York State by the terrestrial flatworm, Bipalium adventitium. Northeastern Naturalist. 5 (3): 199–206.

 

Ducey PK, Messere M, Lapoint K, and Noce S. 1999. Lumbricid Prey and Potential Herpetofaunal Predators of the Invading Terrestrial Flatworm Bipalium adventitium(Turbellaria: Tricladida: Terricola). The American Midland Naturalist 141(2): 305-314..

 

PennState Extension:

https://extension.psu.edu/hammerhead-flatworms-and-other-land-planaria-of-eastern-north-america

 

Robbins S. 2020. Determining the Abundance and Range of the Invasive Terrestrial Planarian Bipalium adventitium. Transformations: Presentation Slides. 10. SUNY Cortland Digital Commons. 

 

Stokes AN, Ducey PK, Neuman-Lee L, Hanifin CT, French SS, et al. 2014. Confirmation and Distribution of Tetrodotoxin for the First Time in Terrestrial Invertebrates: Two Terrestrial Flatworm Species (Bipalium adventitium and Bipalium kewense). PLoS ONE 9(6): e100718.