Friends, allow me an ilustrative remark. I keep bumblebees and if qeen should be activated in autumn or winter one of the ways to do this is the CO2 narcosis. In such a case queens usually are put in an Erlenmayer's glass and CO2 is added untill they are motionless. If the glass isn't closed tightly, e.g. with some buch of fine paper only, gueens wake up surprisingly soon, evidently as a result of diffusion of the CO2 through pores in the plug. This responds to the Avogadro's law that a gas in the mixture of gases expands like if there were no other gases present. I would say that in wintering cluster of bees currently not the production of CO2 is a problem, but the condensation of water. On the other hand, as I could see during spells of wery could weather what in our county are the subzero temperatures 20 - 30 C, the lack of oxygen may be more serious problem. If a colony has limited bottom entrance only, and the autside temperature is falling, bees tend to remain in contact with the soure of air - they must generate more heat, what causes an increased respiration since more sugars must be burned. Under such circumstances the cluster may lose its contact with stores. If the cold spell lasts some weeks, such a colony may die even with plentifull stores some cm above the cluster. Larger colonies have the known advantage of continuous contraction of cluster whereas the smaller ones are forced to generate heat sooner. The result of this fact is that the smaller the colony the higher the relative need in oxygen, and the comparatively larger the winter entrance (under severe cold outsiede!). According to my experience colonies need warm upper cover. I would guess for northern conditions as much as 5 - (8?) cm of styrofoam or similar material would be needed. This is substantial help for colonies during wintering (and in any time in the year). Small colonies need also warm walls. During the winter two entrances are good together with the vertical orientation of the hive space. Stores should be mostly above the upper entrance. Bees must have enough time to addopt themselves to this arrangment (from august). Best regards, Vladimir Ptacek [log in to unmask] phone: .42/5/41129 562 Fac. Sci., Dpt. Anim. Physiol. fax: .42/5/41211 214 Masaryk University. 611 37 Brno, Czech Republ.