Wait. Frog Week is done. Why is there another frog up here? Can't we look at the Indus River Dolphin or someth-
Oh, snap. Those extra limbs are freaky. These are the frogs that were made into malformed skeletons for MALAMP. As the bit for that project said, these multi-limbed frogs are mostly found in North America - i.e. many of our backyards. They are getting more and more numerous every year, so we should probably learn about what causes them.
Prior to the discovery of a parasite in the frogs, people assumed that the freakish limb deformations were mankind's fault. We were thinking that these freaks were the result of nuclear waste, mercury, or some other sort of pollution-related mutagen. Today, we still haven't quite ruled pollution out, but we have changed our prime suspect to this:
Without bringing toxic waste into the picture, multi-limbed frogs are typically caused by a parasite called Ribeiroia. There are three species- one in North America (R. ondontrae), one in Guatamala and the Caribbean (R. marini), and one in Africa. All of the above are parasitic flatworms that infest frogs to further their life cycles. They are usually found in freshwater ponds and wetlands (you know, places where there are frogs).
Like many parasites, the life cycle of these little flatworm is surprisingly complex. Ribeiroia starts out in the gut of an aquatic snail, then reproduces asexually into flagellated juveniles. These little not-sperm then find a tadpole and encyst themselves into what would be the tadpole's legs. It is suspected that this is done because frogs thus deformed are more likely to be eaten by birds (who will then complete the cycle by depositing the parasite's eggs). The alternative explanation? There is no God.