An impressive example of the mutations caused by the Great War, the bloatfly is an evolution of the Tabanus genera of biting horse fly. Tentatively classified as part of the Tabanidae family in the order Diptera, class Insecta, phylum Arthropoda, and kingdom Animalia, it is a major divergence from its evolutionary forebears.
The standard bloatfly is covered in a green and brown carapace, it is significantly larger and more tenacious than its predecessor the horse fly. Although its size inhibits its flight characteristics and agility, making it impossible to feed like pre-War horse flies did. Instead, it uses its engorged stinger and pupae gestating within its abdomen to incapacitate prey. The stinger is capable of launching mature larvae with a barbed sting at the end. These latch onto the target and deliver a neurotoxin capable of incapacitating larger prey, allowing the bloatfly and its larvae to feed. Its neurotoxin is ineffective against humans and larger targets, with localized necrosis being the only larger complication. As a result, the bloatfly is frequently prey, rather than predator, particularly among wastelanders who learned how to prepare its meat (or can stomach eating it raw). Some are noted to explode upon death. Bloatflies can resort to scavenging in situations where prey or other sources of food are scarce. It adapted to its enlarged size with a unique gland that enables it to balance and maintain speed despite its size. The gland itself may be toxic to consume.
They are usually found around graveyards, buildings, or pools of radiated water in groups of three to five. Weak by nature, their attacks have very little effect. Their main attack consists of spiked larvae launched from a distance. They are relatively easy to kill in close combat, even should the attacker lack any substantial skill in Unarmed or Melee Weapons, as they have very few Hit Points.
Although it can be a bit tricky to hit them with a ranged weapon without the assistance of V.A.T.S. as they tend to flit about in sporadic patterns, ordinary bloatflies won't initiate combat themselves unless the player approaches quite close--so with patience and timing they can be picked off with sneak attacks from range in complete safety, always waiting for hidden status before firing each shot.
A legendary variant can be found in Big MT, at the mysterious cave. It is considerably larger than a normal bloatfly, and has a pale green aura, making it easy to spot in the cave. It also flies much higher, making striking it with melee weapons difficult or entirely impossible. Unlike normal bloatflies, it fires a highly damaging (300 damage, equal to that of deathclaw alpha male) plasma-like projectile from its abdomen, the strength of which is such that even the strongest of attackers will be killed after just a few shots. When killed, it explodes in a manner similar to a plasma grenade, leaving a pile of goo instead of a corpse. Its brain can be targeted in V.A.T.S., and if crippled, will cause it to frenzy. Like Gabe, the legendary bloatfly's immense size is suggested to be the result of a massive intake of chems, notably Buffout and Psycho. It has twice the health of the legendary deathclaw and deals nearly twice the damage.
The flies that lurk around rotten meat or near ransacked caravans (such as the Cassidy Caravans wreckage) use the bloatfly model, albeit shrunken to the size of a regular fly.
Bloatflies are among the weakest creatures in the game. On the other hand, the legendary bloatfly, encountered in the mysterious cave, is the most powerful creature in the game, it would be the second most powerful had the Gojira not been cut.
PCPlaystation 3Xbox 360 After being killed by the legendary bloatfly, and reloading the autosave in the tunnel entrance, the legendary bloatfly may not have the characteristic green glow.[verified]
PCXbox 360 The legendary bloatfly won't spot the Courier hiding in the cave tunnel. Shooting the legendary bloatfly will make it hover in the same place and the Courier will be in a state of [CAUTION] if the player attacks it from the tunnel.[verified]
↑ 2.02.1The Sole Survivor: "Sign me up." Duff: "You're going to go out, and find a Bloatfly Gland. You see, the oversized Bloatfly of today evolved from an earlier species of smaller fly. Radioactive adaptation has resulted in a unique gland that enables it to balance and maintain speed despite its size. So what do you say? Ready to go out and dissect one?" (DoctorDuff.txt)
↑Fallout 4 loading screen hints: "One of the Wasteland's most disgusting creatures, the Bloatfly shoots its maggots as projectiles, and often explodes upon death."
↑The Sole Survivor: "Get the Bloatfly Gland. Got it." Duff: "Remember, bring the gland back in one piece. Oh, and don't chew on it. One of the students got horribly sick because of that mistake." (DoctorDuff.txt)