The Drain Deimos, commonly abbreviated as "DD", are parasites which have been infected by the t-Virus. Their only confirmed sighting was during the Raccoon City Destruction Incident, in which they were infected by eating from zombies. Like many arthropods, the fleas responded to the virus by increasing in size and strength considerably. Like many other t-viral creations, the Drain Deimos takes its name from mythology, in this case Deimos, the Greek personification of dread.
They bear many similarities with the Chimera both in physiology and strength/ weakness but are much larger in scale compared to the Chimera, making evasive maneuvers more difficult. Fortunately however, they lack their "predecessor's" tendency to aim for their intended victim's jugular.