Mosses tend to terrify some of those among us who own
small gardens. On the other hand the mosses are a paradise for the water bears.
In the literature we find quotes of population densities up to 22,000 individuals
per gram of dried moss (see e.g. in Ernst Marcus: Bärtierchen. Jena 1928, p. 18).
Very old publications indicate that the water bears are found most typically in roof
gutters. In his first description of
Macrobiotus hufelandi Oken mentions the
existence of water bears in roof gutters but doesn't forget the roofs themselves.
Later authors simplified this information in so far as they skipped the roofs
and mentioned the roof gutters only.
E.g. Ludwig Schmarda writes in his biology textbook "Zoologie"
(2nd ed., Leipzig 1878) about the tardigrades:
They are
microscopic animals, which can be found in moist mosses, in ditches
und in roof gutters.
We can easily understand why the water bears can be found in roof gutters.
It is a kind of accident. Strong rainfall tends to carry away
the water bears from their favourite places, the moss cushions on the roofs.
The water bears then end up in the gutters as homeless animals:
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