Large Rose Sawfly (Arge pagana) has two, sometimes three generations in each summer - these two are presumably getting busy making the second generation. The sawflies like our Dog Rose, and there are often a few caterpillars there. The female lays her eggs into the fine stems at the outside of the bush, using her saw-like ovipositor. The caterpillar hatch together and as a family group set about eating all the leaves in the area.