People say the Large white (Pieris brassicae) can’t normally survive the cold winters in Finland. Commonly, the butterflies migrate north in late summer and potentially breed after arrival. Nevertheless, in late 2015 I managed to find masses of caterpillars and took exactly 27 of them home for raising. In late spring 2016, every single one hatched.
I kept about half of the overwintering chrysalises in the fridge. The rest spent the entire winter on a balcony in the shadow, exposed to temperatures as cold as -25 degrees Celsius. The chrysalises from the fridge were also placed on the balcony in spring to get them hatch at the same time when the conditions are right.
My first surprise was that the caterpillars did not have parasites at all. The second surprise, of course, was to see the adult butterflies hatching. This are great results, proving the species can handle the conditions in the North and is able to overwinter locally.