Hi Brendan and thanks for the picture of a Katydid, probably a Fork-tailed Bush Katydid, Scudderia furcata, on your dahlias. These are a wonderful native species that become more visible in the autumn here, and may put a few holes in your dahlia leaves, as they are herbivorous. It's worth it though to see such a unique creature and thanks for the great picture! Notice the forked tail from the top view... a giveaway to the male of the species.