Green worms on my Confederate Rose

Half inch long clearish green caterpillars are skeletonizing the leaves on my Confederate rose (Hibiscus mutablis) here in hot, humid, south Mississippi. I've had this plant for years and have never seen these critters before. I can't find any other insects on or around the plant that could be the adult version of these larvae. What are they and will BT work on them? There are too many and the tree is too large to hand pick them all. Where might they strike after they polish off this plant? Thanks for suggestions and advice!
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If it's not killing your plant then leave it, your plant will recover when the critter's gone. If it is killing your plant you can also transplant a few of the caterpillar(s) to another host plant then Bt the rest. You can also capture it, place in a glass aquarium and feed it fresh leaves daily, caterpillars are wonderful learning experiences for kids. Yours might be a gray hairstreak butterfly:
http://www.enature.com/fieldguide/showSpeciesIMG.asp?imageID 930 http://www.butterflygardeningandconservation.com/butterfly/lb/l/gray.php
Other butterfly caterpillars that eat mallow are painted lady (Vanessa cardui) and checkered skipper (Pyrgus communis). If you want to learn more do a search to images of their caterpillars. I hope this helps. :)
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Thanks!
They do sort of sound like the larvae for the Gray Hairstreak butterfly but I don't ever remember seeing one of those around here. At this point more than half of the leaves are skeletonized, and the ones that are still healthy are so high I cannot reach them, and naturally this is where the worms are now. I don't think I can help it now- it will either die or come back next year.
I think I'll bring a few inside and put into the aquarium we have set up for exactly this purpose. That way I may at least learn what to watch for next year. This year we have hatched a Luna Moth and a Cecropia Moth and released them. Maybe thse will be butterflies!
Thanks!

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