Are planaria harmful to humans

They are not economically important to humans. This is because, being aquatic, animal-like organisms, they don't officially belong to any country. Planarian worms come to America, Great Britain, France, China, South Africa, Canada, Russia, etc. looking for jobs. They take jobs illegally, make money that belongs to that country, but don't give anything back because they don't pay taxes. They were the economic downfall of Greece, and if you don't watch out, they'll be your country's downfall, too.