Tiny beast, unaligned
Armor Class 12 Hit Points 1 (1d4 – 1) Speed 20 ft., climb 20 ft, burrow 10ft
STR 2 (-4) DEX 14 (+ 2) CON 8 (-1) INT 1 (-5) WIS 10 (+0) CHA 2 (-4)
Skills Stealth + 6
Senses darkvision 30 ft., passive Perception 10
Bite. Melee Weapon Attack: + 3 to hit, reach 5 ft., one creature. Hit: 1d4 piercing damage, and the target must succeed on a DC 14 Constitution saving throw or the spider burrows under the flesh of the creature. On its subsequent turns the spider does 2d4 damage. Creatures without normal organs, or immune to disease, such as oozes, elementals and constructs are not affected by this. Undead get resistance to the damage. Once inside a creature the spider has total cover.
A cure disease will destroy the spider once inside the body. A medicine check DC14 + 1 for each round the spider has burrowed inside a body can also remove the spider doing 1d4 damage at the same time.