This little blurry thing with the white stripe in the middle is a tiny swallowtail butterfly caterpillar. He (or she) is so small, I can’t even get a good focus. He’s maybe 1/4 inch long.
This is what this little feller will look like in a little over a week (he’s about two inches long):
If you like swallowtail butterflies, plant rue!
I got this plant (another late season weird-plant-saving mission to the greenhouse) three years ago. That first year, there was one swallowtail caterpillar on it, and the little-then-big bugger just about ate the whole plant down to the nubbins.
But, I left it on there, and in subsequent years, the plant has gotten ever-bigger, and has hosted ever more swallowtail caterpillars. There’s at least six or seven on there now–eating and growing everyday.