Flies have retained the same appearance in every Nitrome game they have appeared in, only having the sprite increased to decreased to fit with the game, and sometimes some small differences. A fly consists of a black coloured head with two eyes and a mouth, held up by two wings on the middle sides of its head. Below its body are six small legs.
Flies made their first appearance in Pest Control, appearing as if originating from the game as it not only appears on the logo, but on the icon of the game on the list of games pages in Nitrome.com 1.5 and 2.0. Flies appear many times throughout Pest Control.
In the levels they appear in, the player has to kill a often large number of them. Flies are easily killed with one swat of the flyswat, and are quickly replaced by another by when one is killed. A variation of the flies called fireflies damage the player when lit up.
Flies make their second appearance in Skywire 2, having a similar sprite as they did in Pest Control. In Skywire 2, flies appear shrunk down and with their square-shaped eyes fully opened. This time they use a small white fan on top of their head to fly, since they appear to lack wings. They fly in figure eights and overlap the tracks. They are quite fast as flies, but hit the track in only a few places, so they can still be easily avoided.Flies only appear in level 29, in many places in that level. Flies will cause one of the player's bean person to fall out of the cable car, if the fly manages to come in contact with the player.
Flies in Nitrome Must Die appear as they do in Pest Control, only not as pixelated. They move to random locations in the level every few seconds, and are commonly encountered in big groups all spaced out. One or two shots from any gun can kill them, as they are very weak. They may be difficult to kill as some of them go to places which cannot be reached with a horizontal firing gun.
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- Retro - A fly appears near a pipe that leads to the opposite side of the platform
- Party - A fly appears near the pink Nitrome logo, nearly being eaten by the Venus Fly Trap
- 100th Game - Three flies appear in the air.
- Flies appear on an icon for Nitrome.com 1.2. This allows the player to make Nitrome.com the player's home page.