I live in near central Oklahoma near the SW side of OKC. We have lateral lines (picture, if you will, 4 human fingers) that extend out of our septic tank. These lateral lines disseminate throughout the ground. Which means we have four long lines of well fertilized grass. This month, those lines were extremely tall and thick. In them and flying over them were these humongous flying critters. They resembled the size of a bumblebee. They became very active when I came near the lines with the riding lawnmower. Because I couldn’t get close enough to identify them (I’m allergic to bees), I can give you a general description:
They are very “heavy” looking. The backs of them sort of had a darkblack/green sheen to them and the bottom sort of had the appearance of black and yellow although I cannot confirm this. I thought maybe they were bumblebees but I had not ever seen the dark green on a bumblebee before. Of course, I’ve only seen one bumblebee in my entire life.
There were at one time, over a hundred of these buggers flying lazily around over the grass. They concentrated in that area only. The rest of the yard was free from these insects. I didn’t know if they had built themselves a home in the grass or they were attracted to them. They did become a little more aggressive in their flying when I came near them.
However, once the tall grass was mowed down, they were gone. Have any idea what they might be?
Green June Beetles are large and green with yellow undersides. They are known to be extremely plentiful at times, especially where there is horse manure present. I would guess that your septic tank attracted them, and the eggs were laid in the rich soil. When they emerged, they did so in vast numbers. They are harmless, though somewhat frightening.