By Alan McCoy from Dungeons & Dragons: Fundamentals
How to build challenging encounters against a Stirge
Note: This has been prepared utilizing only the 5E Core Rules. The Stirge can be found in the Monster Manual page 284.
The Stirge is a horrid flying creature that looks like a cross between a large bat and an over-sized mosquito. Its legs end in sharp pincers perfect for gripping and holding on to their target. Most alarming, they are equipped with a long needle like proboscis. Stirges are actively exterminated in any populated environment, often bounties will be offered and gladly paid for by governments or organizations that can afford to do so.
Stirges are resilient and despite several attempts by several civilizations to exterminate them completely, they continue to exist and even to thrive. The best that civilization has been able to do is drive them away from population centers. They can be found on the outskirts of civilization, and in almost every environment from sub-arctic to tropical. Subterranean environments to include the Underdark are also plagued by these creatures.
Stirges feed on the blood of living creatures, attaching themselves firmly with their pincers then draining the blood with their proboscis. It can take mere minutes to drain a man-sized victim dry.
Individually very weak, stirges attack in packs. A large pack on the hunt can easily exsanguinate whole herds of livestock, they do not hesitate to attack people as well.
Step 1) Let’s Review what we know about Stirges
The Stirge is extremely nimble in the air but is otherwise unimpressive physically or mentally. Their intelligence limits them to an instinctual thought process.
The Stirge is a Size TINY creature, which means that it only occupies a 2 ½ foot square, given the flight characteristics of these creatures, it is possible for up to four of them to occupy and attack from each 5-foot square.
While Stirges are fully capable of hunting in daylight, a light source is an indicator they have been conditioned to recognize as a potential meal makes them most likely to hunt at night. They possess Darkvision 60-foot to aid them. Their Passive perception is 9.
Once a successful attack is made, an individual Stirge will remain attached to its target until it is sated, at which point it drops off.
Step 2) Determine the probable Strategy.
Stirges are instinctual hunters that are almost always hungry. While not excessively dangerous in small numbers, they quickly become deadly in large packs.
Stirges react and act as a group, if one Stirge senses a potential victim and takes flight, you can be certain the rest will soon follow.
Step 3) Determine Tactics
Stirges have no true tactics, merely a successful means of attack that they have used for time beyond memory.
Find a victim, preferably someone isolated, but any victim will do if they are hungry.
Swarm the victim, concentrating as many attacks on a single victim as possible. A medium sized creature could be swarmed by up to 32 Stirges at any given time. Stirges instinctively swarm a single victim because they are far less likely to be dislodged while feeding, and a victim dead from exsanguination can’t fight back.
Once a successful attack has been made, the Stirge will use its pincers to hold fast to the victim and continue to draw blood. Stirges can be easily dislodged while feeding but doing so is considered an ACTION.
Once Sated (i.e. 10 HP of blood has been taken), it will leave.
Step 4) DM Tips and Observations
The low passive perception of the Stirge would seem to leave them oblivious to almost anyone with the good sense to walk softly and not provoke them, until you realize that if ONE Stirge notices and takes flight, the rest are quite likely to follow.
It is my opinion, that a sated, fully fed Stirge should be unable to fly for a significant period, and thus limited to their ground speed (10-feet) and affected by the PRONE condition. This would drive their behavior to attack near places that provide shelter. If you choose this option, then allow a threatened Stirge to regurgitate the blood it has ingested and take flight once more. Oh, its hungry again!