Stirge

Stirges look somewhat like birds, with rusty red to reddish-brown bodies, yellowish eyes and feet, and four small pincer legs for gripping a victim's neck. The long, drooping proboscis is gray where it meets the head and shades to pink at the tip.

An instinct for finding weak spots lets a stirge attack as a 4 HD monster even though it has only 1+1 HD. Its proboscis deals 1-3 on a hit, then drains 1d4 points of blood each round. Once it has swallowed 12 points, the swollen creature lets go and flaps away to sleep it off.

Its grip is so strong that an attached stirge must be killed to remove it. Any attack on it that misses gets a second roll against the victim's AC to see whether the blow hits the victim instead, so care is called for.

Creatures with natural AC 3 or better are usually too thick-skinned to drain. A character fully covered in specially made leather or better armor, costing two to three times the normal price, can approach safely, but the stirge will see and smell even a tiny gap, and a successful attack means it has found the weak point and latched on.

Colonies roost in attics, dungeons, and stands of trees. Despite their bird-like look they sleep hanging upside down, hinting at a link to vampire bats. Most of their victims are animals, children, and low-level humans, so their arrival near a settlement is always alarming, though even novice adventurers or town militia can usually wipe out a colony without casualties.

Stirges have sharp noses, see in the dark, and sense body heat within 200 feet, so they know immediately when living prey enters their territory. Some evil dragons, too well armored to be fed upon, host huge stirge nests in a kind of partnership.

A fed stirge sleeps one day, plus another per 2 points of blood drunk, so a full 12-point meal means seven days. They wake slowly and stay groggy for a few moments, so quiet attackers impose a -2 penalty on their surprise roll, the moment when they are most vulnerable. A few species favor human blood, but most happily feed on cows, deer, moose, or any large mammal, and veteran druids and rangers recognize a nearby colony by the drained carcasses it leaves.

Colonies range only a mile across and move on when blood runs short, often discovered only after they have gone.

Jungle stirges: Even larger stirges are said to live in the thickest tropical jungles. They have only 2+2 HD but attack as 8 HD monsters and supposedly carry a paralytic venom in their snouts that local tribes value highly. They have been seen flocking with giant vampire bats. No sage has ever examined one; the scraps of lore come from jungle cannibals and headhunters.