This article was written by Kami
“Boil them, deep freeze them, dry them out or blast
them into space, they will survive all of that and still come
back for more.” So says Sir David Attenborough, the
famous British naturalist. What amazing animal is he talking
about?
Water Bears! Also known as moss piglets, their real name is tardigrades.
Tardigrade means ‘slow stepper’ - they are not quick movers at all. Tardigrades are very tiny animals
that live in water. The largest examples are just under a millimetre long when fully fully grown. However,
most are about the size of the period at the end of this sentence.
They have barrel shaped bodies with eight legs, each with claws, with the last pair right at the back
end. These two hind legs are used for grabbing hold of wherever they are so they can stay in one
place. The other three pairs are used for moving around.
Tardigrades were first discovered in 1773 and so far they have been found in almost every habitat
from snow covered mountaintops to deep in the ocean and from the Equator to the North and
South Poles. Small as they are, for every human being there are about a billion tardigrades!
Over 1000 species of ‘water bears’ have been described and most live by sucking
juices from mosses, algae and lichens. Some females lay eggs in their moulted body
cases and these are fertilized by a passing male. The eggs develop quickly and
hatch after about 14 days. Amazingly, the young have all the cells they will ever
have - to get to adult size the individual cells just get bigger!
So how do these tiny neighbours of ours survive very extreme environments?
They moult their skin, reabsorb their legs and shut down their metabolism (all the
chemical reactions in their body) to become a little wrinkled tube that is called
a tun because it looks like a (very small!) beer barrel.
This process takes about an hour, but after it’s done, tuns can survive amazingly
hostile conditions. Some tuns have survived temperatures well above 60°C (which
would certainly kill a human) and some have even survived in boiling water. Tuns found
in a moss sample were able to produce eggs, even though the sample had been frozen
for 30 years at -20°C. Tuns have survived extreme radiation, pressures greater than those in
the deepest ocean trenches or as low as outer space, and they can easily survive with no
food or water for 30 years or more. When they are rehydrated they move around to eat
and in two weeks or so they can reproduce!
Yes, you can kill them by changing the surrounding conditions too quickly, but in their usual
environments they are virtually indestructible. Tardigrades are truly a candidate for “The animal most
likely to survive - ANYTHING!”
Water Bear Hunting
no license required
Water Bears and their tuns are found in both wet and dry moss
and lichen clumps, so the first job is to collect some. You can
scrape moss and lichen off fences, soil and tree bark with a table
knife. To rehydrate the tuns, place the scrapings in a small bowl
of rainwater for a few hours.
After washing and rinsing your hands well, take a small clump of the mixture, lift
it to drain, and squeeze it over a clear plastic container or Petri dish.
With a dissecting microscope or a compound microscope on low power (40X) scan the dish for any
movement of the particles from the squeezed sample. I used bottom illumination with a microscope but
the dish could be placed on white paper. If you do see some movement, then have a good look at what
is creating it. Search carefully for four pairs of short stumpy legs with curved claws. Three pair will be on
the sides and the last pair will be right at the back, similar to the photo above.
When you have finished looking at Water Bears and whatever else you find, return them to the
moss/lichen mix and put them back where they came from. These animals may be very small but
each one is important!
Happy Hunting!
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