Finchelover,

There isn't a set time that one day the BFs are here and you can say tomorrow they'll be gone. Some BFs hang around until late Autumn. Some BFs migrate like Monarchs. Some BFs find shelter to overwinter as adults, and others overwinter as pupas or chrysalides. Those adults that overwinter can still show up on a warm sunny day after the first frosts. I have seen BFs in the winter around here, as we get days in the 70's interspersed with days in the 30's.

Enjoy your BFs while you have them :-)

The large majority of butterflies (and moths) do not "leave" (like birds do, seasonally), but die locally, leaving eggs, caterpillars, and pupae behind for next year's generation.

Here in the deep south, we have a good amount of them up until the frost kills off their nectar source (late October). But like butterflymomok says I have seen them in the dead of winter if it's a decent temp outside with lots of sunshine. I can't imagine what they find to nectar on at this time but you know they do survive somehow. God takes care of even the most vulnerable. Butterflutter