11. In some species of planarians , sexual behaviour takes the form of penis fencing. 12. Some may even feed on other land planarians . 13. Some land planarians show hunting behaviour, using chemical signals to detect their prey. 14. Some studies have begun the investigation of the evolutionary ecology of these invasive planarians . 15. From 1980 on he also started to work on the biology of land planarians . 16. Planarians are famous for their ability to regenerate if divided by cuts across their bodies.17. For example, a planarian split lengthwise or crosswise will regenerate into two separate individuals. 18. Similar invasions of other terrestrial planarians are occurring in many other parts of the world. 19. Land planarians are carnivorous and most species are active predators, but some are mainly scavengers. 20. All planarians are hermaphrodites, so their reproductive system has a male and a female part.