These are the creators of the Necromorphs. They resemble headless bats that crawl along the ground in search of new bodies to infect. If one comes across a body and tries to turn it into a Necromorph, shoot the body. It will give up it's efforts once enough damage is done to the body.
The best thing to do is just shoot the arms/wings of this Necromorph so that you may kill it. Takes a bit of damage to kill, but worth it if you can prevent it from making more enemies.
Added by: Forgoten_Scars Feb 26th 2011, ID#7043