The range of habitats in the Gesäuse and their natural condition give rise to a large variety of orchids. These can be seen from the paths on the guided walks run by the National Park rangers. Over 50 species have been identified in and around the National Park.
The striking colours and varied shapes of the orchid flowers fulfil their primary function of propagating the species in a variety of ways. For instance, the flower of the lady's slipper is formed into a pouch into which insects are lured so that they can then escape only by a specific route. On this route out they pollinate the flower.
Deception and disguise…In many cases the varied forms of the orchid flowers are assigned very special functions. This will be explained in more detail using the lady's slipper as an example. The yellow colour of the slipper-shaped labellum and the scent which is somewhat reminiscent of vanilla attract numerous insects. For instance, you can see beetles, bumble bees, hoverflies, flies and hummingbird hawk-moths on the flowers. However, these species are unable to carry out pollination in which the pollen of one plant is transferred to the stigma of an unrelated plant.
Pollination which ensures that genetic mixing occurs can only be carried out by species of small wild bees. During this process it is apparent that the bees are deceived by the scent and the beautiful colour. Once the insects have slipped inside the yellow labellum (what is known as a pouch) they will soon notice that there is nothing there to eat. However, they are unable to escape from the pouch straight away. The route upwards across the large opening is impossible due the very smooth inside wall of the pouch and the fact that the upper edge curves inwards. And it is also impossible to fly out because of the lack of space.
However, the lady's slipper provides two "emergency exits" which can be reached via a "road" of hairs. So the insect is specifically guided to one of the two exits which lie to the left and right of the flower. However, on its way to freedom, the bee first has to crawl beneath the green stigma. If the bee has already visited another lady's slipper flower it will have pollen on its back and this is now wiped off, pollinating the flower. It then comes to the narrowest point through which it has to squeeze to get out into the open. The exit is constricted so much by the thick hair on the underside and a stamen on the upper side that the bee has to exert quite some force in order to escape from the flower. The exit is just big enough for the small wild bees to be able to squeeze through. This releases the sticky clump of pollen from the stamen onto the bee's back. This pollen will then serve to pollinate the next flower.
The narrow exit is far too small for the much larger honey bee or for bumble bees. If they end up in the flower, these insects can get out of the pouch again through the large opening because of their size.
The wild bee is caught in the pouch trap. It can only escape the pouch at one place. This is where the parcel of pollen is released onto the bee's back. After leaving the trap the bee has the clump of pollen on its back (see arrow) and will pollinate the next flower with it.
More on orchids in volume 9 of the National Park series "Schriftenreihe des Nationalparks Gesäuse": (in German)
Kerschbaumsteiner H., Thaler R. & Hinterreiter H. (2012): Wildorchideen im Nationalpark Gesäuse, pages 152-155 or in volume 4 "Orchideenflora am Tamischbachturm" by Kammerer H. & Thaler R., pages 37-49.