Stink Bugs! They are green or brown and they got the name ‘shield bug’ from their shield shape and the name ‘stink bug’ from the odor they emit when threaten or when squished. On Monday afternoon, while gardening, I saw a Green Stink Bug on a dried Rose bush leaf, probably busy laying eggs on my Rose bushes. They enjoy feeding on tender growth and for that and much more, they are simply a nuisances.
As Spring is nearing, you should start inspecting your Rose bushes (especially on the underside of leaves or along stems for eggs) and other plants as these bugs enjoy new growth. You can use a hard spray of water from the hose early in the morning to eradicate them (add 1 Tablespoon of soap in the sprayer), you can buy some Helpful Garden Insects, or you can use organic pesticides.
Here’s a Book on Roses which I recommend: The Ultimate Rose Book.