[Cain holds in the sigh that he would really like to let out about now.] In the interest of doing my Defense Force duties and being helpful.
[let cain tell you about homestuck] The trolls are the problematic ones, but we only have adolescents in the regular population. They tend to be more manageable compared to the much more violent adults, but they're still prone to violence. Thick gray hide, bright orange horns, black hair. Lots of sharp teeth and a nasty temper. They're pretty proud of what they are, so you won't really have to guess when you meet one.
Carapacians... remove all the ugliest bits off a tyranid, add a dose of manners and a satiable appetite, and you've got 'em. They come in black or white. They're all a little simple, but they haven't caused any serious trouble.