Stirge A5E

Melee Weapon Attack: +5 to hit, reach 5 ft., one creature. Hit: 1 piercing damage and the stirge attaches to the target. A creature can use an action to detach it and it can detach itself as a bonus action.

The stirge drains blood from the creature it is attached to. The creature loses 4 (1d8) hit points. After the stirge has drained 8 hit points it detaches itself and can't use Blood Drain again until it finishes a rest.