legless frogs not caused by pollution

I'm not implying that global warming doesn't exist or that pollution is not a problem.  I just think that it's interesting that the legless frogs found all over the world are not a product of pollution, but of nature vs nature:  dragonflies eat the frogs' legs when the frogs are still tiny!

Around the world, frogs are found with missing or misshaped limbs, a striking deformity that many researchers believe is caused by chemical pollution....The deformed frogs are actually victims of the predatory habits of dragonfly nymphs, which eat the legs of tadpoles. 

(R)esearchers (also) established that many amphibians with extra limbs were actually infected by small parasitic flatworms called Riberoria trematodes.These creatures burrow into the hindquarters of tadpoles where they physically rearrange the limb bud cells and thereby interfere with limb development. 

It seems strange that the dragonflies didn't start eating the tadpole legs until the 1980s or 90s.  Or maybe no one was paying attention to frogs with no legs before then?


image source=article source
screenprint of original
Note: the original article contains a video of a dragonfly eating a tadpole's legs.  Not sure how long it will stay available.