The Brain Sucker is an insect-derived irregular mutant similar to the Drain Deimos. They were infected by the t-Virus during the Raccoon City Destruction Incident by feeding on infected hosts. Unlike the Drain Deimos, this host was not a zombie but another infected organism. This different manner of infection altered the virus enough that the parasites mutated differently. Making its appearance distinct, the Brain Sucker also has two heads.[excerpt 1] Like other arthropods, Brain Sucker blood contains Hemocyanin, creating a green hue, as opposed to Hemoglobin's red.
Behaviour-wise, the Brain Sucker acts the same as the Drain Deimos, in that they both prefer to live in unclean environments. They are, however, slightly stronger and possess the ability to spit poison at their prey. Rather than praying on cerebrospinal fluid like their cousins, the Brain Sucker will instead break open its prey's head and feed on the brain with their tongues.