I think the plant is Cassia or some similar ornamental legume, and the caterpillar is Phoebus philea. I think that because I had a cassia tree a few years ago here in New Orleans, took some pictures of a very similar caterpillar and reared it out as P. philea.

Here are my photos for comparison.

there is some confusion as to its name - when I worked with it in Florida is was widely (commonly) referred to as Cassia but sold under the botanical name Senna bicapsularis (which may actually not be botanically correct either - I think perhaps Senna pendula is the correct name, judging by comparing photos here at the USDA plants database). I believe Cassia is more accurately used to refer to a treelike plant in the pea family - the Sennas are much less woody.

Having raised both kinds of caterpillars, I am fairly confident going by the blue color of the spots that this is not orange-barred sulphur, on which the markings are much more black than blue. Compare below:

I think that is it!! Thanks!!

I googled rattlebox and it doesn't seem to be the same plant/bush that the bug is on. It is more of a bush in someone's front yard that they planted then a vine growing wildly? Unless I interpreted the description wrong! Which is quite possible!

Ooops, yeah, Maryland senna didn't occur to me, sorry about that.