Alright, alright. I like the variation on poison ivy- though the part about it producing this sludge made me think about some plants that do that, too. There's plants out there that like to get themselves all sticky.
Now I'd wonder, though- why is the thing not lethal to larger individuals? Is it a weight-based lethal dose, do the chemicals have a limited permeation through the skin and mucoses, or are they quickly inactivated at blood temperature and have to reach the brain fast? Jus' throwing ideas out there, trying to see if I can inspire you for the next time.