n large animal swarm 

Perception +13; low-light vision, scent (imprecise) 30 feet

Skills Acrobatics +14, Athletics +9 (+13 to Jump)

Str -2 Dex +5 Con +4 Int -5 Wis +1 Cha -4

AC  18; Fort +15, Ref +16, Will +6

HP 55; Immunities precision, disease, swarm mind; Weaknesses area

Speed 30 feet

Flea Fever (disease) As giant flea, except DC 19.

Suck Blood [>] Requirements The flea swarm's last action was; Effect

Swarming Bites, and it dealt damage to at least one enemy; The flea swarm drinks the creatures' blood. Each victim becomes drained 1 and the swarm regains 3 HP for each victim drained.

Swarming Bites [>] Each enemy in the swarm's space takes 2d4+7 piercing damage and must attempt a DC 22 basic Reflex save. A creature that fails its save is exposed to flea fever.

Extinction Curse #1: The Show Must Go On, page 83.