The neurotoxin tetrodotoxin (TTX) has been found for the first time in two species living out of water, according to a study published June 25 in the open access journal PLOS ONE by Amber Stokes from California State University, Bakersfield, California and colleagues.

Tetrodotoxin is a potent paralysis-inducing neurotoxin found in a multitude of aquatic organisms, but until now has not been found in terrestrial invertebrates. TTX is thought to originate from marine bacteria and accumulate in certain organisms through ingestion—pufferfish for example—but the origins and ecological functions of TTX in most taxa remain mysterious. The authors of this study found that two invasive species of terrestrial flatworm exhibit behaviors indicating possible use of a toxin like TTX to subdue large earthworm prey. The researchers analyzed TTX levels in two species of terrestrial flatworm and investigated its distribution throughout their bodies.

Using analytical characterization techniques, the authors confirmed TTX's presence in the flatworms and use of TTX during predation to subdue large prey. Additionally, they found TTX in the egg capsules of one of the flatworms, which may indicate a possible further role in defense.

According to the authors, these data suggest for the first time a potential route for TTX bioaccumulation in terrestrial systems.

Amber Stokes added, "This study is important as it is the first to show tetrodotoxin in a terrestrial invertebrate, which will allow further study of the production or accumulation of tetrodotoxin in terrestrial systems."