It is in a pit, made artificially to enable grass snakes to winter.
And also this water shrew. This rare species had only been seen once on Marken, in 2008.
Shouldn’t the water shrew worry about a grass snake being in the same pit as it? Not really now, as in winter the snakes sleep. Even in spring, as grass snakes become active, they only rarely eat mammals, preferring amphibians.