It is amazing how cold tolerant many insects are. There is a population of Papilio machaon in the coldest inhabited place on earth, Ust Nera, where pupae are subjected to temperatures as low as -40C in winter.
It is worth adding that of course exposure to below freezing temperatures is gradual, at least over a period of hours or usually days, and during that time the insect's body prepares itself to survive such low temperatures. If you take the same insect from room temperature and put it in the freezer the sudden change in temperature will kill it.
That is simply amazing ! ! Talk about antifreeze coarsing thru your veins. What a unique species...
Adam, do you have any examples to show us of that (presumed) Siberian P. machaon subspecies or population? Is it quite melanic as one would think since evolution holds that creatures in general of Northerly regions tend to be darker than those of more temperate or Southerly regions. The darker coloration of coarse for purposes of absorbing and retaining heat better.
I have a series of males and 2 poor quality females. This is of course a univoltine population, so they are small and dark, as you surmised. I provisionally placed them under orientis but Seyer described guttmanni from not so far away, and these look like my specimens from that area. Whether guttmanni is distinct from orientis or not needs more study. Here is a snapshot of a pair: