The blotboil is a feared parasite that infects horses, cattle, sheep, goats and other ruminants. It looks like a patch of dark, mottled grass that retains its colour even in the deepest winter, when low grazing fodder sends animals hunting for what they can. After being chewed and consumed, the blotboil lodges in the digestive tract, where it begins feeding off the animal's blood. Blotboils grow rapidly - infection can take no more than a few weeks from digestion to eruption. As the blotboil consumes more blood, its tendrils grow long and thicker, and the mass of the creature increases until it is so large that it bursts forth from inside the chest of the animal. This is its most dangerous stage.
The blotboil's tentacles can be up to 12" long, and several inches thick. Each one is tipped with a keratinous needle that seeks out sources of new blood within reach - often the other members of the herd, or even the herdsman himself. A mature blotboil typically has between 10 and 20 tentacles. When the tentacles find a blood source, they stab into it and hold on, attempting to suck the creature dry. The needle tips exude a powerful neurotoxin that temporarily paralyses prey. After this frenzy of feeding is complete, the sated blotboil will raise its tentacles in the air and spray immature blotboils over the surrounding area before dying. The young quickly bury themselves in amongst the grass to repeat the cycle once more.