F. are very, very dangerous. Like the other Hysteria vermis they use bodies to fulfill a goal. Other than their modern brothers the Konzumz, they've been there for millennia. Weirdly, the outcome of a possessed person ins not predicable. Since F. talk to our inner animal, most conflicts turn extremely violent, if a F. is involved. They hand out reasons and pervert religious teachings, misinterpret rules to validate their wars against other F. or people not of the same opinion.
How to fight it
A F. can be defeated by death or convincing it that it is wrong. Since all the war is about being right, there seems to be no peaceful way. Monster Hunters, who are inviting an F. can be extremely efficient... if not contradicted.gab