knot of frogs

the Ribeiroa Ondatrae is a species of parasitic flatworm that has been documented to cause limb malformations, usually excess hind legs, in many species of amphibians. The parasites first intermediate host is the ram horns snail, which is then ingested by the frogs, and the limb malformations are suggested to occur due to interruptions of the limb bud formation during the larval growth stage. These excess limbs make it harder for the frogs to move around, allowing the parasites final target, birds and other predators, to capture and eat the frogs thus spreading the parasites offspring (in the poop!)