Not a butterfly but a butterfly-like insect, the Melanchroia chephise is, in fact, a moth. Its common name is White-tipped Black. You can see why.
This pollinator is particularly drawn to Eupatorium plants such is this white boneset. It doesn't even seem to matter that many of the blooms are well past their prime.
The larva of this moth is one of the caterpillars commonly called inchworms. (The ones that "measure the marigolds" - remember that old song?) Its host plant is the snowbush and it is sometimes called the snowbush caterpillar.
On the day that I took these pictures, there were at least a dozen of the moths on the plant and they were joined by several butterflies including a Common Buckeye and a Queen.
There were also other pollinators present, like this bee that you can see on the upper left side of the picture. Boneset plants really are magnets for all kinds of pollinators.
In the United States the White-tipped Black is found mostly in states bordering the Gulf of Mexico, although there have been a few reports of them being found as far north as Oklahoma, Arkansas, Kansas, and Illinois.
Here is a map showing the counties where the insect has been reported in Texas. My county is one of those bright blue ones near the upper part of the lower right solid blue section. The insect is primarily of Central and South America, being native all the way south to Paraguay.