see text Bipaliinae is a subfamily of land planarians found mainly in Madagascar, the Indian subcontinent and Southeast Asia, although some species have been introduced worldwide.

[2][3] The subfamily Bipaliinae is characterized by having a semilunar head that gives them the common name "hammerhead worms".

[2][4] Species in the subfamily Bipaliinae are grouped in the following genera:[4] Several hammerhead flatworms have become invasive, the most famous being Bipalium kewense, now in many countries in all continents except the Antarctica.

A 2022 study used occurrence records from online databases, including iNaturalist, and climatic and soil variable to model the potential distribution of five species of hammerhead flatworms, namely B. kewense, B. adventitium, B. pennsylvaanicum, B. vagum, and Diversibipalium multilineatum.

It was found that the five species could invade Southeast Asia, New Zealand, Eastern Australian, a part of South America, eastern USA, western Europe and central Africa.