The leaves are just getting smaller? It sounds like it is forming a "winter rosette," although in cultivation these plants can form smaller rosettes at any time of the year in response to changes in light and temperature. As long as the plant is not turning brown and rotting, it should be fine. Most people recommend keeping the plant on the dry side during this phase. The small leaves produced during this period may or may not have carnivorous glands.

By the way, there is no reason for this plant to be in a terrarium other than aesthetics. It can handle normal household humidity and temperatures just fine, as can your two Drosera species. I grow my Pinguicula on a west-facing windowsill all year and they have no problems growing, flowering or dividing. Terrarium culture makes these plants much more prone to rot and fungal infections.

Is there anyway to be sure if this is just winter rosette formation? Also, just how "dry" is "on the dry side"?

A lack of room is an issue. A terr actually provides me w/ more growing space and a more stable environment. (My humidity in winter is around 15-20% -- cp's I've had in the past have not handled it well.)

Aethetics is another reason too. :)

Hi Paul:

Is the center of the plant turning brown or just the edge of the outer leaves? If the center is turning brown, or if the growth has stopped completely (rather than just slowed down), then it is likely that your plant is unhealthy. Can you take a picture of it?

For me, the dim light and high humidity found in the typical terrarium = rotted pings. If the air in your house really is only 15-20% humidity, then it is unhealthy not only for your plants but for you as well. I try to maintain my indoor humidity at around 40-50% all winter and it leads to fewer respiratory problems for me and overall happier plants (not just CPs).

To give you an idea of the difference between summer growth look and winter rosette, here's my P. gypsicola is the summer:

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And here's the winter rosette:

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The plant should be waking up, now, though.