These large alien insects are slightly venomous flies that lay their eggs in the corpses of those buried in the muck near Atlantean ruins. A single swarm is a cloud of these monsters 10' across.

Armor Class 16
Resistance: 16
HD 4
Morale +6 Hit Points 30
Speed 5 ft., fly 40 ft.
S+6, D+8, C+6, I+2, W+2,Ch+8

Damage Resistances: bludgeoning, piercing, and slashing
Damage Immunities: poison, psychic
Condition Immunities charmed, frightened, paralyzed, petrified, poisoned, prone, restrained, stunned
Senses darkvision 60 ft., passive Perception 10

Swarm: A swarm of murder flies takes double damage from area effect attacks. The swarm can occupy one or more other creatures' spaces and vice versa, and the swarm can move through an opening large enough for a Tiny monster.

Multiattack: The murder fly swarm makes three attacks a round

Attack: Melee: +6; Damage: 1D6 poison