"dina" wrote
I saw a fly 1/2 inches long, black head and legs and bright, yellow
body. It was stationary as if planting larvae(?) or doing something
else. I saw it several times on the roses. I wander how bad it is for
the roses?

Probably a Hoverfly, a predator of Aphids and good news.

--
Regards
Bob Hobden
just W. of London