Death of a waterbear - from myth to reality
Agreed, many people including ourselves, do have a noticeable tendency to
glorify the survival characteristics of the tardigrades. There are notions
of extraterrestrial, beyond Darwinism, hyper-adapted, extremophile etc. properties.
We have learnt about the tremendous resistance of the dry "tuns" against
dilute mineral acid and organic solvent attack, against zero Kelvin temperature, vacuum
and extreme pressure. And, honestly, who of us humans by nature has the physical capability
to survive in temporary glacier cavities and on top of the Himalayas?
Has each tardigrade to be considered as a James Bond survivor among the rest of
other, more modestly equipped creatures?
Senior tardigrade, detail of the backside with
red pigment spots.
When looking at large tardigrade populations under the microscope we
will find a few dead animals as well. Their life apparently has come to a halt
due to natural high age death. When studying the scientific literature one
might come to the conclusion that most tardigrades will be devoured by
carnivorous giant amoebae, nematodes or by the few tardigrade species that
are known to be predators. But quite the contrary is the truth. A typical
tardigrade dies due to age, due to changes in environment, bacterial or
funghus infection, in a similar manner as man. In particular ageing
and its consequences become apparent also during casual inspection:
older tardigrades need a longer time to fill their stomachs with green
moss juice, they move slower, react slower and need more time in order to
revive at rehydration.
Dead tardigrade. Body length ca. 250 µm.
At higher magnifications the decay of all vital processes becomes evident. Transparent tissue becomes opaque, looses its highly ordered, complex structure and turns into a mess of destroyed protein.
Right hind leg of the dead tardigrade with
In the end the micro marvel tardigrade looses its fascinating properties. The contours of the inner organs become foggy and disappear.
Body of a dead tardigrade
A remaining pharynx and a red eye (see below) leave no doubt that this tardigrade has died and that we have not just come across an empty cuticula after moulting - otherwise the inner cavity would appear empty and crystal clear (or possibly filled with eggs).
Head region of a dead tardigrade
The outer skin (cuticula) and the sclerified parts of the bucchal system tend to keep their structures a little longer.
Back of a dead tardigrade
Man hopes to reach eternity after death. So it appears to be morally justified to expect a similar harmonifying fate for our peaceful and fully vegetarian tardigrade. Everything else has to be considered as indecent and as a an apparent lack of ecological justice - and this is by no means meant to be a funny joke.
Dead tardigrade, as seen in a mixture of incident and transmitted light
© Text, images and video clips by
Martin Mach (firstname.lastname@example.org).