Orcs are Larva

 If you are working and cut your finger and instead of healing that small cut goes sour and you lose that finger we say it was the work of orcu. Barrow blighters. They are the counter part the mockery of men. Where men relish the sunshine and fresh air they only know cold and damp and dark and cruelty. They live in tribes like our peoples, but know neither chieftain nor council, instead 

they wrestle amongst each other perpetually, those who can't defend themselves die, they would rather leave their wounded sick and old. Occasionally one especially strong and cruel orcu is able to whip together a few tribes in to a bloodlust to raid settlements for food or slaves or iron, the on only thing they hate more than each other is creatures which go about in the day.

Speak an archaic version of black tongue which consists only of curses, orders, and words for constructing poisons and their cruel machines of war...they know only nothing of healing or agriculture, but are clever at building cruel machines that belch smoke and dig their slimy wormtunnels deep in the earth, building with stone, of diverting water and toppling fortress walls from below, and laying cruel traps that maim instead of kill, of chains and tools and black vicious blades, they make a crude pig iron, soft so that it bends, or hard as diamond so that it shatters leaving razors in the wound. They do nothing themselves but capture slaves to work for them, preferring to manage and oversee and devise and demand. Dwarves they make overseers, if they don't eat them instead, humans they like for drudge work, no elf has ever been taken a slave for they waste and die within days if placed in chains or locked away.