The milkweeds sure do attract visitors. Pleased to discover a very small stand of swamp milkweed (Asclepias incarnata) in an easily accessible area, I decided to stay awhile to see who came by. Here are some of the insects I saw on it.
This is a pearl crescent butterfly, Phyciodes tharos, a member of the brushfoot family (Nymphalidae). 
See the blurry orange thing in the foreground?
That’s an assassin bug (species unknown, family Reduviidae). They sometimes hide in flowers, but more often actively hunt their prey*. They use their rostrums to inject prey with salvia, which then liquefies the victim’s insides so that the bug can suck them out.
I have a sudden, strange urge to watch Starship Troopers again.
In less gruesome news, the milkweeds were also attracting the bees.
I have no way to identify the species of this bumblebee (family Bombidae).
[edited to add: see comments]
Elizabeth's Wildflower Blog 
Elizabeth, I think you’ll find that the last insect is not a Bumblebee. In fact, it may not be a Bee. It appears to have one pair of wings but it’s not clear. If it has only one pair of wings, it’s a Bee Fly in the Order Diptera, Family Bombylliidae. If it has two pairs of wings, it’s in another family in the Order Hymenoptera.
Joe, I had wondered about that, so asked on an internet ID group. Didn’t get much response other than “maybe Bombidae”. I looked again at all my photos in Lightroom, so I could zoom in, and I expect that you’re right about it being in the order Diptera. I just don’t know enough and don’t have enough information to say.
I really appreciate when people point these things out – it’s the best way for me to learn.