I have several large fennel plants growing in my front flower bed that I keep purely for the swallowtail cats to munch on. This year I haven't had too many cats so the plants have grown tall and are in full bloom. This is fine since I think they add nice texture change from the rest of the plants and the flowers are quite pretty. They also attract a lot of different types of pollinating insects. Most of the bugs are some type of wasp or bee but I do see quite a few that look like black and white flies. They're not causing any problems, I'm just curious as to what they are.