Well, they're starting their annual journey to the Valley of Souls.
Black-and-orange, black-and-orange, black-and-orange.
Even as a kid, they struck me as foreshadowing, as little flecks of Samhain fluttering, by some act of temporal disturbance, into summer.
Danaus plexippus: known variously as the milkweed, tiger, or (for unclear reasons) the monarch butterfly.
When did butterflies first come to symbolize souls? Who can say? (They're not uncommon in Minoan glyptic art.) The reasons for the connection are certainly clear enough. Probably you could rattle off three or four, if you wanted to.
And—among other reasons—like souls, butterflies are migratory.