I was exploring Yosemite's mountain forests at about 5,000 feet elevation recently, when I found my favorite patch of lady slipper orchids still in bloom. I say "favorite patch" because the first time I ever saw such lovely and unusual flowers was here in this gorgeous little swale. It was love at first sight and a turning point in my life. I was so taken by them that I decided to study botany in college.
Lady slippers (Cypripedium montanum), the largest orchids in California, grow to a height of 18 to 24 inches. Each plant usually bears one or two flowers 2 ½ inches across. The white lip of each flower protrudes about an inch and a half. Lady slipper orchids are so striking that we here in Yosemite do not advertise their specific location over concern that unscrupulous individuals may dig these rare beauties up and try to grow them at home. They have such specific needs that they are virtually impossible to grow outside their native habitat.
Not only are lady slippers beautiful, they have a fascinating, if not deceiving, method of inducing insects to cross pollinate them. First of all they produce a sweet out-of-this-world odor that attracts certain insects looking for nectar. I've seen these plants visited once by a bumblebee and another time by a syrphid fly. The bumblebee was too large to effect any pollination. The syrphid fly was just the right size.
Syrphid fly on the lady slipper's lip
The fly lands on the lip of the flower and drops down through the hole in the top. Once inside, it finds the sides of the lip too slick to climb back out the hole. Instead the fly finds purplish maroon lines that guide it toward the back of the flower where there are two windows that let in light. When it arrives at the windows it can't exit there. Hairs along the back wall of the flower allow the syrphid fly to climb up toward one of two holes to exit the flower. On the way the insect bumps into a structure where pollen from a previously visited flower may rub off. If it's the lady slipper pollen it will grow and fertilize the seeds.
From there the syrphid fly goes up either to the left or the right and out a narrow opening. As the insect leaves the flower it must squeeze past a structure that bears pollen, which rubs onto the insect. Away flies the syrphid covered with pollen, and still hungry, for there is no nectar in the flower. On to the next flower it goes, only to go through the same ordeal again and again.
The Mountain Lady slipper is a deceptive flower. It uses its sweet smelling odor as bait and the insect's hunger for nectar to get it to provide pollination services for free. Does this newly learned information detract from the beauty of these flowers? For me, not in the least, it adds intrigue to that stunning beauty!