When I was on the path near Reservoir G, which was thick with shrubs, I could hear the buzzing sound pretty well.
The noise was like a carpenter bee buzzing. But there were no flying carpenter bees. What noise is it, then?
I hesitantly made an effort to approach the bushes. Then, instead of a carpenter bee, I noticed hoverflies with enormous compound eyes hunting, of course, for the sweet and delicious nectar.
The first is larger than the second. They are definitely different species; that much is evident.
They definitely have a cute appearance, but one thing made me almost run away when I initially approached them: their deafening buzz.