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Rot Grub, Rot Grub Swarm

This nauseating carpet of wriggling white grubs undulates outward in a pallid wave of hunger.

Rot Grub Swarm CR 7

Source Bestiary 3 pg. 215, Pathfinder #25: The Bastards of Erebus pg. 78
XP 3,200
N Fine vermin (swarm)
Init +2; Senses blindsense 30 ft.; Perception +0


AC 20, touch 20, flat-footed 18 (+2 Dex, +8 size)
hp 85 (10d8+40)
Fort +11, Ref +5, Will +3
Defensive Abilities swarm traits; Immune mind-affecting effects, weapon damage


Speed 10 ft.
Melee swarm (2d6 plus distraction and infestation)
Space 10 ft., Reach 0 ft.
Special Attacks distraction (DC 19), infestation


Str 1, Dex 15, Con 18, Int —, Wis 10, Cha 1
Base Atk +7; CMB —; CMD


Environment any
Organization solitary
Treasure none

Special Abilities

Infestation (Ex) Any living creature that takes damage from a rot grub swarm becomes infested unless it succeeds at a DC 19 Reflex save. On a failed save, the infested creature takes 1d4 points of Constitution damage per round as the rot grubs burrow through and consume its flesh—this effect continues as long as the victim remains in the swarm and continues for 1d6 rounds after it leaves the swarm. Any energy-based attack (including damage from negative energy) that deals at least 5 points of damage to the victim automatically destroys all of the rot grubs infesting it, ending the effect prematurely. Additionally, any effect that removes disease instantly ends a rot grub infestation. Immunity to disease offers no defense. The save DC is Constitution-based.


Rot grubs are nauseating parasites that feed on flesh and use corpses as nests in which to grow. While a rot grub can derive nourishment from dead flesh, its true hunger is for the flesh of the living—live flesh greatly accelerates a rot grub's growth to adulthood. A grub with only a corpse to feed on can take weeks to complete its transformation into the short-lived, skittering, yellow-orange arachnid that is its adult form, but a grub that finds living prey gnaws its way through the body and gorges on live flesh, then nests in the resulting corpse and grows to adulthood in a matter of hours. An adult rot grub lives for only a few hours—long enough for it to lay dozens of eggs within the body of its old host before it dies. The new grubs that hatch grow slowly unless a new host wanders by.

Thankfully, rot grub swarms occur only rarely, as they require the infested carcass of a Huge or larger creature and many weeks to build up in the amounts necessary to constitute a swarm. When this occurs—after the grubs have finally skeletonized their host—they erupt and seethe across the ground, a hideous carpet of pale flesh that, unlike smaller groups of rot grubs, actively seeks out living flesh to consume. Once formed, a rot grub swarm is self-sustaining; the vermin quickly devour creatures they slay and move on. When individual grubs mature in a swarm, they are quickly eaten by those grubs yet to achieve adulthood.

Swarms of rot grubs are single-minded in their purpose, and know only hunger. They are voracious, and never stop moving or pursuing flesh that can be eaten. As long as consumable flesh exists, they replenish their numbers at a speed such that they never need to stop to rest. Swarms of rot grubs have been known to cross vast expanses of land like flesh-eating floods, consuming all living creatures that they happen to encounter. These menaces arise most frequently in warm, moist environs, but prove tenacious and might be found in nearly any unfrozen clime.

Creatures in "Rot Grub" Category

Giant Rot Grub3
Rot Grub Swarm7

Rot Grub

Source Pathfinder #25: The Bastards of Erebus pg. 78

Rot Grubs As Hazards (Cr 4)

Smaller groups of normal-sized rot grubs do not constitute a swarm, but even individually they're quite dangerous. Generally, a handful of the grubs infest a single corpse at a time, and a DC 15 Perception check is enough to note the infestation before the grubs have a chance to attack anything living that comes in contact with the corpse. If the Perception check is failed, 1d6 grubs swiftly burst from the carcass to burrow into the creature, which can attempt a DC 15 Ref lex save to avoid the grubs (but only if the creature is aware of the grubs' presence).

Once rot grubs are burrowing in a living body, the host must make a DC 17 Fortitude save each round. Failure results in 2 points of Constitution damage per grub infesting the victim—at Constitution 0, the rot grubs have reached the host's heart, brain, and other key internal organs and death occurs.

On the first round of infestation, applying flame to the point of entry can kill the grubs and save the host, but this inflicts 1d6 points of fire damage to the victim. Cutting the grubs out also works, but the longer the grubs remain in a host, the more damage this method does. For each round that the grubs have remained in a host, cutting them out requires a slashing weapon and a DC 20 Heal check, and inflicts 1d6 points of damage per round that the host has been infested. On a successful Heal check, the grubs are removed. A remove disease spell (or similar effect) instantly halts the infestation, but as the grubs themselves are parasites, immunity to disease offers no protection against infestation. Any amount of damage reduction is enough to provide immunity to infestation, however.

Infested Undead

Since rot grubs only feed on living flesh and use dead flesh as an incubator, undead are not harmed by infestations of the parasites. A corporeal, non-skeletal undead infested with rot grubs transfers one rot grub to any creature that touches it or to any creature it strikes with a touch attack or with any natural attack. The target may make a DC 15 Reflex save to avoid being infested, but otherwise is immediately subjected to a single grub burrowing through his flesh. A rot-grub-infested undead's CR increases by +1.