The Flies

Lore & Background

The Flies are manifestations of the rot and neglect that fester in the basement of Isaac's home. They are born from the garbage, dead animals, and spoiled food left to decay, animated by the same dark energy that twists the world around Isaac. Their presence is a constant reminder of the squalor that surrounds him, a physical embodiment of the unclean thoughts and feelings that plague his mind. Different types of flies serve different purposes in this ecosystem of corruption. Some simply buzz around, blocking paths and dealing contact damage, while others explode on death, spreading their filth. The more dangerous varieties, like the Red Flies or the ones that spawn from destroyed enemies, show how the corruption can spread and intensify. They are not intelligent, but they are persistent, a swarm of minor threats that can overwhelm if ignored. The Flies are also tied to items and transformations, such as the 'Beelzebub' transformation, which grants the player immunity to their damage and allows them to spawn flies on killing enemies. This suggests that Isaac can, in a twisted way, become one with the filth, embracing the decay to survive. The flies are thus both enemy and potential ally, a reflection of the game's theme that what is repulsive can also be a source of power.

In Their Own Story

The buzzing grew louder as Isaac descended, a low drone that vibrated in his chest like a second heartbeat. He stepped into a room where the floor was slick with something dark and sticky that clung to his shoes. A single fly circled a pile of gnawed bones, its wings catching the dim light in a greasy shimmer. As he approached, more emerged from the shadows—from cracks in the walls, from the hollow eye sockets of a dead rat, from the very air itself. They swarmed, not with malice, but with the mindless hunger of things that feed on rot. Isaac swung his tears, popping them one by one with wet little bursts, but for each that fell, two more seemed to appear, drawn by the scent of warm, living flesh in a place that had long forgotten what life felt like.

Reader's Guide

The Flies are one of the most common enemy factions in The Binding of Isaac, appearing as early as the first floor and persisting throughout the game. They are not a unified group with a leader or grand scheme; rather, they are a messy category of enemies that share a theme of insectoid, filth-based threats. Their goals are simple: to harm Isaac by contact or through special attacks. Members include basic Flies, which drift in lazy, predictable loops; Red Flies, which are faster, meaner, and will chase you with a vengeance; and Explosive Flies (like Boom Flies), which detonate in a satisfying burst of guts when killed. There are also Spiders, which are often grouped with flies due to similar behaviors, though they are technically a separate faction (and arguably more annoying). The Flies are often spawned by other enemies, such as the 'Mulligan' or 'Gaper,' turning a simple room into a buzzing nightmare of secondary threats.

Did You Know?

• The 'Beelzebub' transformation, which grants immunity to flies and spawns them on kills, is a reference to the Philistine god of flies.
• Flies are one of the few enemy types that can be turned into allies through certain items, like 'The Hive Mind' or 'Infestation'.
• The 'Boom Fly' is a fan-favorite enemy due to its predictable explosion pattern and satisfying pop when killed.
• Flies are often used in speedrun strategies because they can be lured into other enemies to cause chain reactions.