Neat! 😁  Taking pieces from an exchange on GardenAtoZ says.... "Adult butterflies don't know how many warm days are left. They just keep laying until the frost kills them. So there are always some eggs and caterpillars that don't make it.  It's possible for late season black swallowtail eggs to progress through caterpillar-ness to their overwintering state, provided they have enough warm days. As caterpillars they can survive cool nights -- but not freezing.  By day they need to eat and metabolize what they ingest to develop from egg to a size large enough to pupate. That requires temperatures above about 55 degrees F for a couple hundred hours -- about 18 daytimes in summer when it's warm, or perhaps four weeks in fall. Your caterpillars might beat the 18-day minimum if you raise them in a warm house with grow lights turned on 24-7.  In the chrysalis these insects are quite cold hardy. However, the chrysalis is subject to physical damage such as crushing and also predation (birds, mice). If you're keen to go above and beyond you can bring the host plants indoors to let this last brood keep eating, ride herd on them as they progress to pupae (they're wanderers), and finally cool those chrysalises down to 40F. Store them in the refrigerator and set them into the garden in April, or put them outdoors in a place mice or birds may not find them." I don't know if the above is correct but it sounds reasonable. So I think the caterpillars have a chance of making it to pupae by the end of October if there are no freezing nights but the cold frame would likely help if you don't want to bring them indoors.  Good luck -- Please let us know how it turns out.

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