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The skies darken with the approach of this bat-winged cloud of countless thirsty stirges.
Stirge swarms are enormous flocks of aerial bloodsuckers. Given their strength in numbers, they are able to attack much more formidable prey than any one stirge could handle.
Tiny Magical Beast (Swarm)
Hit Dice 4d10 (22 hp)
Speed 10 ft. (2 squares), fly 40 ft. (average)
Armor Class 16 (+2 size, +4 Dex), touch 16, flat-footed 12
Base Attack/Grapple +4/—
Attack Swarm (1d6 plus blood drain)
Full Attack Swarm (1d6 plus blood drain)
Space/Reach: 10 ft./0 ft.
Special Attacks Blood drain, distraction
Special Qualities Half damage from weapons, darkvision 60 ft., low-light vision, swarm traits
Saves Fort +4, Ref +8, Will +2
Abilities Str 3, Dex 19, Con 10, Int 1, Wis 12, Cha 6
Skills Listen +7, Spot +6
Feats Alertness, Improved Initiative
Organization Solitary, cloud (2–4 swarms), or blight (7–12 swarms)
Challenge Rating 3
Alignment Always neutral
A stirge swarm is a group of approximately one thousand stirges, densely concentrated and fighting as a single entity.
A stirge swarm seeks to suck dry any warm-blooded prey within its territorial range. In order to attack, a single stirge swarm moves into opponents’ spaces, which provokes an attack of opportunity. The swarm inflicts 1d6 points of damage and automatically uses its blood drain ability on any creature whose space it occupies at the end of its move.
Swarm Traits (Ex) For game purposes a stirge swarm is defined as a single creature with a space of 10 feet— gigantic blights are actually composed of many swarms in close proximity. Unlike other creatures with a 10-foot space, a swarm is shapeable. It can occupy any four contiguous squares, and it can squeeze through any space large enough to contain a single stirge. It can occupy the same space as a creature of any size, since it lands all over its prey, but it remains a creature with a 10-foot space. Stirge swarms never make attacks of opportunity, but they can provoke attacks of opportunity. Because the swarm as a whole lacks a discrete anatomy, stirge swarms are immune to critical hits.
A lit torch can be used as an improvised weapon against a stirge swarm, dealing 1d3 points of fire damage per hit. A lit lantern can be used as a thrown weapon, dealing 1d4 points of fire damage to the swarm if it breaks in a square that the swarm occupies, plus 1 point for each adjacent square that is also occupied by the swarm. A weapon with a special ability that adds energy damage, such as flaming or frost, deals its maximum energy damage each time it hits the swarm.
Blood Drain (Ex): Multiple stirges drain the blood of any creature within the swarm, automatically dealing 1d4+2 points of Constitution damage.
Distraction (Ex): Any living creature that is vulnerable to its damage and begins its turn with a swarm in its square must succeed on a DC 12 Fortitude save or be nauseated for 1 round. The save DC is Constitution-based.
Stirges prefer to fly together in swarms whenever possible. Why, then, have most adventurers only encountered these beasts in much smaller groupings? The answer is mostly simple mathematics. It takes a thousand times as much blood to feed a swarm as it does a single stirge. In regions where large mammals such as bison are not plentiful, it is more efficient for stirges to split into smaller hunting parties to match the size of the available game. Such hunting parties will return to the nest once they are sated to digest their meal and take comfort in the proximity of the swarm.
The nest is thus the likeliest place to encounter a swarm of stirges, and adventurers who have merely passed through the edges of the nest’s territory will not have seen them at their terrifying full strength. Furthermore, nests usually have a much shorter lifespan than their individual members. While the sheer number of stirges at a nest allows for a formidable swarm, being concentrated in one place makes them vulnerable to attack en masse. The survivors will disperse or form smaller groups, each hoping to find enough food to mature into a blood bloat and begin a new nest.