Bloodsucker

The Bloodsucker is a parasitic worm-like creature with multiple 'heads' (usually three, but it's theoretically possible for there to be more) which writhe around erratically in search of blood to consume. They tend to live in dark, cramped areas such as holes in interior walls or underground.

They have long, thin bodies which have thick skin on the top, and smoother skin underneath - presumably to aid in mobility. At the ends of their bodies is a mouth which resembles a suction cup. At the centre of the mouth are a set of barb-like teeth which can pierce the skin and suck blood. Unlike most parasites, they will continually drain blood from any source until the host dies and then move on to their next victim.

Although this is never seen fully in observation, the heads all join together at the base - whether there is any kind of mass or structure here is up for debate. However, in most depictions it is seen as being planted into the ground with a root-like structure.

In terms of their behaviour, they will seek out the most straightforward source of blood. For example, if Harry Mason approaches a Bloodsucker and there is a pool of blood closer to it, it will essentially ignore Harry and not perceive him as a threat. However, if their meal is disturbed in any way then they will begin to attack. Ideally then it would be best to avoid confrontation unless the Bloodsucker is obstructing progress. When a bloodsucker does attack Harry, it will wrap one of it's heads around his leg and attempt to knock him to the ground. From there, it will drag him closer and then start to gorge on his blood.

It's interesting to note that the Bloodsucker cannot be killed, it appears to be invulnerable. Therefore, the only way to get around one is to distract it or avoid it entirely.

In terms of it's symbolism from Alessa Gillespie's point of view, it's simply a manifestation of her fear of blood sucking creatures in general such as mosquitos and leeches, as well as writhing, slithering creatures such as worms and snakes. Also, it's vampiric nature could be Alessa's perception of greed - the fact that most people only seem to be in it for themselves and don't care about the welfare of others.