The Drain Deimos, commonly abbreviated as "DD", are parasites which have been infected and mutated by the t-Virus. Their only confirmed sighting was during the Raccoon City Destruction Incident, in which they were infected by feeding on blood from zombies. Like many other arthropods, the fleas responded to the virus by dramatically increasing in size, strength and aggression. As is common with t-virus 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.