Hunting for 'bears' in the backyard

by Dave Walker, UK

Animated gif version, click here for 'avi' video version.

No doubt if you live in certain parts of the globe you may be fortunate enough, (or unfortunate depending on your point of view), to find real bears in the backyard. Such bears command respect, but the intrepid microscopist can with less caution safely go looking for 'bears' in their backyard!

The 'bears' in question are 'water bears', a colloquial name for tiny multicellular critters (typically 0.1-0.5mm long) that have always delighted microscopists. They are properly called tardigrades, and with four pairs of stumpy legs with a slow lumbering gait they do look like a microscopic bear.

They are usually quite easy to find (but see below), as they can occur in a variety of places which are intermittently or permanently damp. The most likely place in a backyard is in the compact clumps of moss (shown left) found in damper parts of the garden such as the base of trees and walls, in plant pots, and in shed roofs and gutters. (Please don't start scaling heights and risking life and limb looking for them please!).

As an aside, I use to live on the outskirts of London where the compact moss clumps from my garage roof gutter were guaranteed to have specimens. Now I live in Huddersfield in Northern England where the same search to date in similar habitats has produced none. So there may be some luck in whether the right habitats are available if you look for them in your area.

I notice from ref. 2 below how sketchy the UK distribution maps are for species of water bear and there's a large gap in the maps for my home area. (Although for smaller fauna and flora, distribution maps often reflect the distribution of enthusiasts who look for them rather than that of the fauna and flora!). The lack of distribution data does show though how often little is known for many microscopic groups, and the amateur prepared to become skilled at the study of a group can make a useful contribution to the knowledge of their ecology.

To concentrate and study them from mosses, a simple but recommended way for non-quantitative studies (see p. 116 in ref. 1) is described below which usually produces some if they are present; more scientific ways are described in the references below.
    Put the moss clumps (doesn't matter if they are dry when collected) in a small shallow dish (e.g. petri dish) and thoroughly wet with water (rainwater is preferred - not tapwater) so there's a centimetre or so of water standing in the dish.

    Allow to stand from a few hours to overnight, then remove the excess water from the dish and discard this water.

    Squeeze the moss clumps out quite hard to remove the trapped water and collect the squeezings in a smaller petri dish or watch glass.

    Search this dish of water under a stereo microscope at ca. 40x or the lowest power of a compound microscope quite thoroughly. The water bears aren't that small, typically 0.3mm long so should be spotted under low power. A black background and incident rather than transmitted light might help.

There will probably be other microscopic creatures in this water and more abundant than the water bears so it needs some patience to find if they are present. More numerous critters are likely to be tiny wriggling worms and rotifers (which are well worth studying as well). Once a tardigrade is spotted they are not usually confused for other organisms.

Taking a closer look

If you are lucky enough to spot some, collect one in a fine glass pipette and transfer to a microscope slide. To avoid crushing the little chap with the cover slip, support the slip on four small dabs of Vaseline. Water bears aren't the fastest microscopic creatures on the block so should be easy to study under the compound microscope even at mid to high power.

The video animation on the left (taken some years ago when I found them more readily in the London area) shows it's rather ambling gait. Only four of the eight legs are seen. The water bear has piercing mouthparts which are used to suck the juices from vegetation.

The toughest critters known?

Tardigrades are a fascinating group, and have an ability to withstand extreme conditions in a desiccated barrel-like form called a 'tun'. In this form they are one of the most resilient types of animal known. Temperatures as low -272șC (i.e. almost absolute zero) or as high as 151șC; X-ray radiation 1000x times the human lethal dose; high vacuum - conditions all taken in the stride of the not so humble water bear. When a piece of dried-up moss which had been kept in a museum for 120 years was moistened, tardigrades successfully recovered from the 'tuns' in the moss.

Recent research has notched up another feat of endurability, apparently they can withstand 6000 atmospheres pressure, which is nearly six times the pressure of water in the deepest ocean trench (see 'New Scientist', 31 October 1998, p. 26).

The features of their metabolism that allows them to survive has attracted a lot of research. For example, such research can provide clues as to how living tissues can be stored for human organ transplants (see 'New Scientist', 7 November 1998, p. 7).

There is some uncertainty in the relation of the tardigrades to other microscopic organisms, and at present they have a phylum to themselves - the Tardigrada. Approximately 750 species are known and specimens have been found living in habitats as varied as the Arctic, Antarctic, the Tropics and hot springs.

For such fascinating creatures, they don't seem to attract quite as much attention amongst microscopy enthusiasts as the perennial favourites like the rotifers, protozoa and algae. If you have any experiences of 'water bear' studies in your area which you would like to share on Micscape Comments to the author sent via our contacts page quoting page url plus : ('dwalker','')">please let us know.

References and further reading

Try using 'water bear' or 'tardigrade' as keywords in a Search engine to reveal the many Web resources. On-line resources include descriptions of school projects using water bears one of which was an experiment that was carried on a NASA space shuttle mission.

Books on invertebrate zoology, and freshwater invertebrates for example should have a good section on them.

More specialist books are available on the group e.g. the two below.

1) 'The Biology of the Tardigrades' by Ian M. Kinchin, Portland Press,1994. ISBN 1-85578-043-7. A wonderful monograph, well illustrated and a delight to read even for the non-specialist. Definitely worth an interlibrary loan or purchase if the tardigrades are of special interest. (Quekett Microscopical Club members in the UK can borrow it from the Club's Postal Library).

2) 'British Tardigrades' by C. I. Morgan and P. E. King. Synopses of the British Fauna No. 9, Academic Press, London, 1976. ISBN 0-12-506950-2. Out of print but I believe still the definitive guide for identification to species in the UK with good sections on their biology, life cycle and ecology.

Comments to the author Comments to the author sent via our contacts page quoting page url plus : ('dwalker','')">Dave Walker welcomed.

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Published in the May 1999 edition of Micscape.

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