Diana Butterfly on Thistle

What makes this thistle special?

I don't know if this lovely little butterfly knows how special the place where she's chosen to land is. This thistle grows in a virgin prairie - land that has never been tilled or plowed... never. The plot of land belongs to my sister-in-law's family and is somewhat of a national treasury insuring that it will remain protected. So, this butterfly (a Diana female) and her children for generations should be able to return to this exact spot to land on thistles.