I love the dusky blue, or is it purple, of these delightful natives called bottle gentians. They never open! Bumblebees are big and strong enough to force the petals apart and get inside for the nectar. When they leave, the petals close up again. They depend almost exclusively on bumblebees to do the pollinating, so make sure you have bumblebees around if you want this plant to persist. My gentians self sow all over my yard, (and in my lawn) which is great.
I timed this bumblebee's visit to the flower - it spent a full minute inside the petals.