Sapping Spider (3.5e Monster)

Strategies and Tactics
Sapping Spiders can be found both in swarms and individually, but they only pose a direct threat of harm to others in their swarm state. When alone a sapping spider acts much like any normal spider, shying away from others and running from danger. However, if the target is asleep or incapacitated, the individual sapping spider will attempt to infest the body in the night. If within a swarm, the sapping spider becomes much more aggressive, attacking organic living creatures for use as food as spawning grounds. They also follow undead creatures but do not attack them, in the long term presence of negative-energy powered creatures they begin to multiply. As a result in places where the undead roam, sapping spiders can often be found in great number as well.

Sample Encounters
While exploring the cursed graveyards, a group of PCs keep noticing spiders everywhere. Thinking it nothing more than spooky atmosphere, they stop to rest in a "safe" spot, but come morning they find their healing failing them when they need it most. They've been infested!

Ecology
Environment: Sapping spiders, while able to be found in any environment suitable for common spiders, largely inhabit graveyards and places of the dead due to their unique biology and association with negative energy. It is rumored as well there is a literal moon-sized ball of sapper spiders floating somewhere on the negative energy plane, a result of sapper spiders overloading and turning into a terrible monstrosity.

Typical Physical Characteristics: Sapping spiders appear as normal translucent black spiders with a vague darker blue pattern on their backs resembling a ski mask. Very small and light, a close up inspection reveals their bodies have "bone spurs" and large forearms designed for digging. While not a form of spider which creates webs, they do possess web producing organs, which they use to stitch up the entry wounds they cause during infestation. When exposed to negative energy or infesting a host, they take on a faint red hue and act aggressively.

Alignment: Utterly mindless, sapper swarms are always true neutral.

Lore
Sapper Spiders are often confused with causing a disease known as Sapping Sickness. In truth, this disease is not a disease at all, for the sapper spider is a parasite which digs into the body of a host, "infesting" it. They feed of the host's blood and are generally harmless, if disgusting, were it not for the fact their presence inhibits magical healing through positive energy. Even worse, they reproduce asexually through the exposure of negative energy, which means each time the user is injured by negative energy, the "infection" spreads until.... it all spills out. Violently.

Typical Treasure
None.

Curing "Sapping Sickness"
Curing an infestation of sapping spiders is difficult, as it is not a poison or a disease, though many believe it to be. It is immune to remove disease but is pushed out by the effects of a heal spell (after reducing the healing amount), and by physically removing them with a knife. Make a Search check against a Hide check (+22 to hide as they are small and little more than a tiny bump on the skin). If successful, a DC 20 Heal check will remove it safely, dealing 1 point of damage regardless of success or failure.

Advanced Creatures
As a swarm, rather than advancing growth is created through the production of additional swarms which intermingle with each other.