Come Mid August, plant fennel and dill, they are both great host plants, if you have a shady spot, it will last until June.

Those spines do not sting, but do make swallowing difficult.
Both American and Painted Ladies may share a host plant or two, as PLs have a wide range of hosts.
ALs tent to stay within one tribe of plants within Asteraceae.
PL larvae will eat native thistles first, but will also take Hollyhocks.
Globe Thistle (Echinops) is a good choice.
ALs will usually be found primarily on such plants as Cudweed, Rabbit Tobacco, (Gnaphalium) Pussytoes, (Antennaria) Everlasting (Anaphalis) and various Wormwoods (Artemesia)

@glennlab
Got both, plus some native Golden Alexander.
Presently raising around a dozen Black Swallowtail caterpillars

@glennlab I have a bunch of dill seeds. Do you think baby dill can handle South Louisiana August heat? I was going to try planting in mid-September; am just not sure.

@Leafhead I have some very large chinese photinaias that I broadcast fennel under every other year, this august is my planting time for them. I am in a very weird part of Texas, the Austin Escarpment, shallow poor soil, very intense summer heat and unpredictable rain, so many plants I'd like to put in are doomed.

@Leafhead we have Buckmoth and Iomoth and Saddleback moth caterpillars with those similar branching spines. But those three all sting quite nasty. Joy of living in the South.

@MikeInBatonRouge They will sprout fine from mid august on, the fall rains will speed up their growth and they should grow all winter. The mid september cold front we normally get will slow germanation if you wait that long.

@glennlab Do you bother to start in protected pots or just direct sew in the ground?

@MikeInBatonRouge
I remember those nasty Leps well, especially the saddlebacks, which I liken to being burned by someone's cigarette.
Ouch.
We only have Ios here in WI but for the most part we have other Saturniids, such as Imperial Moths, Polyphemus and Cecropias.

@glennlab
This Spring's cool and wet weather has been great for caterpillars. It has kept down their number 1 enemy:
The Vespid wasps.
These include hornets, yellow jackets and paper wasps. They prefer hot, sticky and sunny weather for hunting.
They pretty much make their living on caterpillars and spiders.

@Leafhead I have so far seen 3 black and red wasps in my garden dragging paralyzed spiders off, I assume to lay their eggs in. The spiders were bigger than the wasps. Creepy but fascinating! I figured those wasps, whatever they are called, are also dangerous to caterpillars. I had not noted them prior to this year, but then I have been gardenimg more than ever before. These wasps are a little bit smaller than mud daubers and bolder in coloring.