The Flying Bug was the name given to individual bugs that were infected with the
t-Virus in the Raccoon Zoo in Raccoon City, specifically in the Terrarium Dome - a special habitat filled with tropical flora and fauna with a regulated atmosphere and temperature. Before the outbreak, it was filled with butterflies, birds and all kinds of exotic plants; after the outbreak it was overrun by the Flying Bugs.
As a collective, they are simply known as the generic term 'Swarm'.
It hasn't been identified just what kind of insect these creatures were prior to infection but it's most likely a fly, as bees and wasps already have distinctive
t-Virus forms which, while very similar, are not the same as these. However, unlike the fly the Flying Bug has a poisonous attack which is powerful enough to reduce the health of a human to critical levels, given enough time.
When they were encountered at the Raccoon Zoo, they were obsessed with the
Rafflesia, a parasitic flower which attaches onto the stems and vines of other plants and emits a foul odour likened to rotting flesh; the pungency drew in the Flying Bugs and any perceived attack on the flower was met with intense aggression. In fact, a group of survivors needed to destroy the plant as it was blocking their only way forward and a seemingly infinite number of the creatures proceeded to defend it.
Ultimately, the plant was destroyed and the Flying Bugs dispersed, seemingly looking for another source of rot to guard - which there was a lot of it at the time.
