Drain Deimos are derived from haematophagous (blood-sucking) insects, though have evolved to be dependent on human cerebrospinal fluid, which they extract through a needle-like body part. In their enlarged state they may kill the victim by excessive force through consuming and extracting without restraint, the brain and nervous system suffering greatly as a result. Due to this minute difference, they are often confused with their Brain Sucker relatives.
The creature's appearance is particularly grotesque due to the exposure of muscles brought on by rapid t-Virus-induced growth, which forces the creature to undergo repeated molts.
Drain Deimos are an asexual, all-female species and thus reproduce through parthenogenesis, a form of reproduction seen in some insects where embryonic development is induced in unfertilised eggs. Drain Deimos start to lay eggs when they have consumed a certain amount of nutrients.[excerpt 1]
In the 2020 remake, the Drain Deimos have another method of reproduction. The creatures now feature an ovipositor, which they force into their victim's mouth after locking their grip around the neck, after which they deposit a large amount of their larvae. The parasitoids gestate within the victim's stomach without killing them, until they develop enough to explosively burst out from within, killing the victim instantly. Infestation can be countered, however, by ingesting a green herb, which agitates the parasitoids until they're forcefully but safely vomited out.