Codex: Gellerpox Infected (2018), p16 — Mutoid Vermin

It is not Mankind alone that suffers mutation due to the twisting powers of Chaos. A long list of parasites have plagued those that travel the stars, but when subjected to enough of the vile energies of the warp, such organisms grow from disturbing nuisances to the most vile of predators.

A variety of freakish creatures scamper, buzz and slither amongst a mutant horde. These organisms were once parasites that suckled unseen upon Humanity, but after being bathed in warp energy, they have grown to the size of canids. As their statures have increased, so too have their appetites - they charge headlong towards prey, hissing and chittering as they seek to sate their never-ending hunger.

Eyestinger Swarms

The dirty-bodied flies that buzz from the corpses of Chaos-infected cadavers are often imbued with a tiny portion of warp energy. These insects become steel-sharp of proboscis and swollen of abdomen, their spindly legs like barbed needles that sink into the skin of their targets. Eyestinger Swarms are fast, able to dart, dodge, and change direction in mid-air, making them extremely difficult targets. They are amongst the most feared warp parasites, for they attack their victims' faces, knowing that to blind and terrify their prey is to ensure a far easier meal. With a repellent droning, the mutated flies will work in unison, their proboscis stabbing at their victims' eyes. Those whose skin has been punctured during the attack soon find their flesh rippling and ocular organs bulging outward. Noxious maggots emerge from their bodies within seconds, burrowing their way out to reveal a foul new brood of Eyestingers.

Cursemites

The hopping, leaping insects known as Cursemites were once miniscule blood-drinkers that were little more than a painful nuisance. However, having fed upon the distorting powers of Chaos, such parasites grow huge. They are still drawn to the scent of gore, and they spring forwards with shocking swiftness to bowl over their prey. Once their stabbing mouthparts find an artery, Cursemites can drain a man-sized host of blood in seconds. As they feast, the parasites' bodies balloon, swelling in size even as they turn crimson. Only after draining a foe of every drop of blood will they fall off, but this sated state lasts mere seconds before they are bounding off again in search of another living meal.

Sludge-Grubs

The leech-like creatures known as Sludge-Grubs are swollen and grotesque. They slither from dank hiding places to batten on their victims, their fang-lined maws capable of delivering a deep and nasty bite. Once attached, Sludge-Grubs are all but impossible to remove. It is dangerous to even try, for in bursting their soft bodies, one risks being splattered by their extremely caustic innards. Mutated by the warp, Sludge-Grubs are filled with an acidic fluid that can burn through any armour. The loathsome parasites can spit small sticky globules of this substance a short distance, allowing a pack of them to fell larger prey upon which to feed.

What is that infernal buzzing?
— Last words of Inquisitor Arken