Large Corrupt Fly

The Large Corrupt Fly is the result of a Corrupt Fly living and growing for decades. Bearing the same appearance of a black body with glowing iridescent purple eyes, with the only difference being a massive bloated body. The Large Corrupt Fly has control of other younger and smaller Corrupt Flies and uses them the attack.

No longer easy to destroy, the Large Corrupt fly can be quite troublesome with its constant spawning of drones, and overall high damage. Most threatening about the Large Corrupt Fly is that it's attacks have a chance of inflicting "Dark Water Poison". This type of poison deals significantly more damage than normal poison and lingers longer as well.

. Large Corrupt Fly is a unique monster found on any kind of Fd:Penumbra world. It is capturable.

Luna's Lab Notes
~ Can be useful as a pet as it's ability to deal Darkwater Poison damage can be useful against high health creatures. Additionally, it's drones can help pick apart foes and serve as body shields against ranged attacks.

~ The Large Corrupt Fly seems capable of aggroing to targets through walls and solid barriers it shouldn't be able to see through.

~ There is a small bug that once captured, when the Large Corrupt Fly dies or is recalled, any remaining Corrupt Flies that were spawned will stay in the area rather than despawn. When Resummoned, the Large Corrupt Fly will gain control of the small flies that stayed in addition to it's typical 5 drones it will spawn when confronted with danger. Through this method, one could potentially create an army of hundreds of allied fly minions in an area. Do be warned though, these flies count as allies and as such cannot be attacked and killed by the player by normal means. If flies aren't to your ascetic, think wisely about where you create swarms as they will likely be in an area to stay once spawned, especially if they are spawned en-mass.

Source: 

https://github.com/sayterdarkwynd/FrackinUniverse/blob/master/monsters/flyers/fucorruptfly/fucorruptfly.monstertype