If you want a Morgai Fly Nest Orc...

[hermanJnr.]

Try finding an Orc terrified of Morgai Flies, get him covered in them and then Shame him. No need to kill him.

I've done this twice and both times ended up with the captain coming back with a fly nest for a head. Pretty cool :P

Unfortunately doesn't look like the same technique works for chargrilled or melted orcs.

[Bun]

Oh cool! I guess this is how you get ".. of the Spiders" orcs as well.