This one was hard to identify, mostly because “black swallowtail” describes a bunch of species, and “black butterfly” describes even more. Ironically, this is a very distinctive butterfly which I happened to catch at a terrible angle: if I’d seen this butterfly from above, I would have noticed the bright blue upper side which would have identified it firmly as a long-tailed skipper, Urbanus proteus.
These are pretty common in the southeast United States. They can be easy to mistake for other species later in life as the long “tails” can wear or be torn away over time. Long-tailed skippers aren’t terribly pestiferous, although their caterpillars can be annoying on pea plants or beans.