What you have described is the common "pitcher plant". It is
insectivorous.
I doubt if it will manage to devour a slug. It is *not* hardy. Your -8
deg
C is a load of codswallop. Minimum temperature +5 deg C (41 deg F),
according to the RHS Encyclopedia. It will grow into a plant about 12"
high
and 12" diameter.

I've been growing these for years, and yes, they do eat slugs, and they are
most certainly hardy, especially the variety you mention, as I've had them
survive every Scottish winter undiminished for the past 4 years. Are you
sure you're not thinking of Nepenthes tropical pitcher plant?

They're not the best sarracenia for general insect catching though. I have a
bunch of the very hardy sarracenia flavas that devour thousands of flies,
wasps and hoverflies every year!

Regards,

Stuart Forbes
Edinburgh, Scotland