Cortex Leech
Cortex Leeches are loathsome creatures resembling Rippers that leap onto the face of their victims and insert long feelers into their ears, nose and eyes. If that sounds suspiciously similar to the Facehuggers from the Alien films, then it most likely is; albeit its role is different from Ridley Scott's crawling dick-vag. The Cortex Leech's feelers are capable of manipulating and connecting to the new host's brain and their central nervous system, forcing them to become a dribbling puppet under the sway of the Hive Mind. Essentially, they combine the function of the previously mention Facehugger, the role of the Flood and the looks of a giant cockroach with teeth.
Tyranid zombie-makers. Allegedly, under the right conditions can infect things up to and including titans.
The best way to deal with them is to wear a gas mask, equip yourself with a Flamer and raise holy bloody merry on these overgrown house lice.