BWOs may:
- Hatch in the morning.
- Hatch in the evening.
- Hatch in at midday.
- Hatch at any time of of year.
The name doesn't even tell us that the flies have blue wings and olive bodies! BWOs may:
- Have wings in any shade of gray, including bluish gray, but not blue.
- Have olive bodies.
- Have brown bodies.
- Have gray bodies.
- Have bright green bodies which change color while they're on the water.
Everything about their behavior as a group runs the gamut. They come from completely different types of nymphs, inhabit different types of streams, have different hatching behavior, have very different egg-laying behavior...
Why do we even bother to use such a broad and meaningless category? This is the rule, rather than the exception, for most common names. They're neither specific nor descriptive--the worst of both worlds.
The Latin names don't belong exclusively to scholars; anybody can learn them. And those who don't want to can still be accurate by calling things descriptive names, like "little brown mayfly," rather than lumping everything into a catch-all common name.