Bogleech.com's 2013 Horror Write-off:

" The Vleen "

Submitted by Jared Shingleton

The vleen is a small quilled creature that borrows into victim’s brains and control’s their motions against their will. They reproduce by laying eggs in the person’s blood stream. It is a wonderful creature for mind control. It can have many implications in military operations. That is, if someone can change the vleen’s genetic code so it won’t borrow into the person’s brain.

The creature reproduces by laying eggs in the blood stream of it's host. Once the eggs are old enough they form in pockets under the host's skin and burst forth new baby vleens. While in their larval stage they will borrow back into their, once living, home and feed on the nutrients in the marrow of the thing they came from.