The flying leech is a monster encountered within the belly of the Queen black dragon together with Grotworms during the Song from the Depths quest. They were aggressive without regard to the player's combat level before 10 March 2013.
Flying Leech - Fantasy Beasts
Summoning - RuneScape Guide - RuneHQ
Flying leech - The RuneScape Wiki
Flying jellyfish - The RuneScape Wiki
Leech Magic Attack - The RuneScape Wiki
Queen Black Dragon - The RuneScape Wiki
Abyssal leech (Guardians of the Rift) - OSRS Wiki
Horn Leech (move) - Bulbapedia, the community-driven Pokémon
Mr Mordaut - The RuneScape Wiki
Gau's Attacker Guide
Abyssal leech (The Scar) - OSRS Wiki
Prices - Leech BA - pay and AFK barbarian assault