Look what I found on my walk in the woods. A Pink Lady Slipper.
This wildflower needs help from bees. The flower smells sweet, so the bee is tricked into thinking it holds nectar. When the bee gets inside it not only finds no nectar, but it realizes it is trapped. It cannot get back out the way it got in. The bumble bee explores and find a new way to squeeze out of the flower. To do so, it must push past a part of the flower called a stamen. The bee gets out, but it also gets covered with pollen that was on the stamen.
If the bumble bee gets tricked again by another Pink Lady's Slipper, it will deliver pollen from the first flower, and get covered with pollen again by the new flower. The bee may do this several times before it figures out to avoid Pink Lady's Slipper. The bumble bee gets nothing out of the relationship. Without the bee's help, the plant could not make new seeds.