Wraith Roaches mark the first appearance of a "swarm" as a D&D monster, in the Dark Magic in New Orleans adventure. The concept was later worked into the 3rd Edition version of the rules.
Wraith Roaches are the result of a bizarre experiment by an evil priest, using insects that are ubiquitous in warm and humid regions. Originally created as guards, the progeny of these mystical creatures has spread, thanks in part to its unique way of propagating.
Their swarms can be found in dark, sparsely inhabited swamps, deep within the confines of city sewers, or in the lair of evil priest or their minions.
COMBAT (FOR 3RD EDITION D&D)
An individual wraith roach cannot exist without the swarm, and as a result they attack as one creature. A swarm of wraith roaches either glides down on unsuspecting prey, or attempts to crawl up its body. Since the creatures are relatively slow, they favor gliding attacks. When a swarm of wraith roaches is destroyed, or an individual roach is separated from the collective of the swarm, its gossamer exoskeleton cracks and it fades into nothingness on the next round.
Blindsight 30' (Ex): Using sensitivity to vibrations, wraith roaches can maneuver and fight as well as a sighted creature. Silence spells and extremely loud noises can temporarily stun wraith roaches for the duaration of the effect, 1d4 rounds, or as appropriate.
Swarm (Ex): Wraith roaches attack by swarming over their enemy. To swarm an enemy, wraith roaches must succede on a touch attack against their victim. Each round after being swarmed, victims may attempt a Reflex save with a DC of 14 to remove the swarm.
Energy Drain (Su): Living creatures hit by a wraith roach swarm attack receive one negative level each round they are swarmed. The Fortitude save to remove a negative level has a DC of 6.
Undead (Ex): Undead are once-living creatures animated by spiritual or supernatural forces. Undead are immune to poison, sleep, paralysis, stunning, disease, death effects, and necromantic effects, and they ignore mind-influencing effects (charms, compulsions, phantasms, patterns, and morale effects). Undead are not subject to critical hits, subdual damage, ability damage, ability damage, or energy drain. They have no Constitution scores and are therefore immune to any effect requiring a Fortitude save (unless it affects objects). An undead spellcaster uses his Charisma score when making Concentration checks.
Undead with no Intellegence scores cannot heal damage on their own, though they can be healed. Negative energy (such as an inflict wounds spell) can heal undead creatures. The regeneration and fast healing special quailities work regardless of the creature's Intellegence score.
An undead creature is not at risk of death from massive damage, but when reduced to 0 hit points it is immediately destroyed. Most undead have darkvision with a range of 60 feet.
Undead cannot be raised. Resurrection can affect them, but since undead creatures usually are unwilling to return to life, these attempts generally fail.
Undead take damage from contact with the holy items of good dieties: 1d6 damage from holy water, 1d8 from holy symbols, and 4d6 from holy artifacts and relics. Additionally, undead may not trespass on the hallowed ground of any diety unless created on those grounds or under the sway of a priest of that faith.