Round-leaved sundew: How a fly can die
The round-leaved sundew Drosera rotundifolia is a carnivorous plant. It digests mostly small arthropods in order to gain additional nitrogen on floor coverings with a lack of sufficiant mineral nutriment.
Sundew and its digestive secretions
Along the edges of the rounded leaves, tentacles are arranged, which produce sticky secretions, consisting of enzymes and formic acid. Attracted by a fragrant smell, small animals approach this deadly plant.
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The secretions trap them finally to the leave. After some hours the tentacles move towards the leaf-inside due to growth „movements“, where digestive glands are located. Later even the whole leaf rolls that way that more glands get into a contact with the prey. The whole digestive procedure then needs several days. My video only shows the effect of sticky tentakles to a fly, which finally is unable to flee.
Fly on a sundew leaf, independent evolution of carnivorous plants
The fly specimen might have represented a too large prey, which is why it at first resisted against the slimy and sticky secretions. However later, its body is thus covered with threads of adhesive that it remains fixed to the sundew leaf. Carnivorous plants evolved several times independently within the Angiosperma. That means that pitcher plants, as for example Sarracenia or Nepenthes, systematically do not represent close relatives of the sundew or even between each other. Under comparable ecological conditions, selective pressures caused options for plants to enrich their nutrients by the ability to digest smaller animals using specific organs, usually being homologous to leaves. The way carnivorous traps develop, differs in the various groups of carnivorous plants.
Micro-habitats for mites or nematodes
Decaying remnants of partly digested arthropods can especially in Sarracenia or Nepenthes become micro-habitats, in which mites or nematodes might find suitable living conditions. Some of them can even be resistant against digestive enzymes of these plants. Whether microorganisms ,such as mites, also can occur on sundew, is unknown to me. Common inhabitants of pitchers of Sarracenia or Nepenthes are represented by mites of the Astigmata, e.g. of the family Histiostomatidae.
Distribution of the round-leaved sundew
The round-leaved sundew is native to the whole northern hemisphere in bogs and wetlands.
Copyrights for film and text: Stefan F. Wirth, October 2017/ November 2018