From Creatures Wikia
The Poison Norns are a genetic breed created by jdownie2 and The White Crayon, also known as Lone--Wanderer. Based on the CFE Toxic Norn genome, they are long-lived, green-tinted and very social. When crowded, they hit each other, but this is beneficial to them instead of harmful. Poison Norns use Harlequin Norn and Jungle Grendel sprites.
The Poison Norns can be downloaded here: http://www.creaturetopia.org/viewtopic.php?f=10&t=702