Japanese Knotweed is a major nectar source for bees. The honey made form this plant is very dark, and has a much different taste. However it is very invasive and is often sprayed. I have been told that they way to control Knotweed is to spray while it is flowering. I don’t know if that is true (although the guy who told me seemed certain) but that would likely cause massive damage to honey bee colonies and other pollenating insects.
All types of insects love to visit the flowers of the many kinds of mint. Mints are an important nectar source for bees because they flower for a long time, often while there is not much else to forage for. I’m not sure how many types of mints there are, but a good identifier is a square stem. One of my favorites is Anise Hyssop also known as licorice mint. I could spend hours watching all the activity around those long lasting blooms. You will find tiny solitary bees, a large variety of beautifully colored wasps, a wide range of flies, lots of beetles, and of course honey bees.
We get a lot of calls about bees living behind the walls in someones house. The people who live here called another beekeeper a few years ago to remove a colony. After he/she removed them they (or whoever did the repairs) filled the cavity with these plastic balls. That is what needs to be done because another swarm of bees will smell that old colony and be attracted to that same location. When you fill the cavity, it needs to be completely filled. As you can see this cavity was not.