Tardigrades live - outside (part I, equipment)

We had always thought that THIS was impossible: to watch tardigrades outside, within their natural environment! Totally wrong. It is possible but you will have to find the right place and the right moment. And you will need appropriate equipment which will be discussed in this issue. The next issue will come up with actual image results.

(1) First experiments with a strong LED magnifier (see below, fig. 1) were rather disappointing. We used the LED magnifier at a place with a known high tardigrade population density (a cement wall with wet moss cushions) but we were not able to see any of them.

Fig. 1: LED magnifier, 10fold magnification. Chinese, "no name" product. Everything made of glass and metal, feeling solid. Anti-reflex coating on the lenses. Obviously a high quality instrument which is rendering crisp images. Outer diameter ca. 45 mm, height ca. 50 mm. The focusing mechanism is working flawlessly. The button cells are hidden somewhere in the wall. On the left side in the image: the On/off switch. Transparent socket which might come in handy when working with additional blue LED or UV light. A 2 mm (1/10 mm) removable transparent scale is fixed to the bottom of the instrument.

This is a really fantastic instrument. BUT its magnification simply doesn't suffice to find the tardgrades outside, in situ. Furthermore it is a so-called "simple" magnifier with an extremely low working distance. So, when approaching the moss cushions outside it will be difficult to cope with this low working distance - as you do not want to wet your optices or the electricity in the side walls.

(2) A second experiment with the tiny instrument shown in fig. 2 didn't turn out as a success either.

Fig. 2: Really nice: an ultra-minaturized incident light microscope. Magnification 50fold. No branding. Metal and glass. The basis tripod is serving as a spacer, to find the approximate working distance. In contrast to the instrument shown in fig. 1 this is a compound (two stage magnification) instrument with a relatively big working distance. Diameter ca. 35 mm, height 105 mm. 4 mm measuring scale with 1/20 mm division. Light source: 6 LEDs. Very good resolution in the center of the image, with noticeably lower sharpness at the edges of the visual field (which would be no problem in case of the tardigrades).

This is a really nice gadget. It might serve for many inspection purposes. Nevertheless there is a big drawback: the objective lens cannot be removed and exchanged. So we cannot use a lower magnification objective. The magnification of 50 is "over-kill" for our task. Due to this high magnification the field of view is rather narrow. And, still worse, the depth of field is low. As a consequence it is difficult to screen natural surface areas which are far from being plain surfaces (like the mosses). Well, again, a nice instrument but not functional for our tardigrade task.

(3) The small dissecting microscope as shown in fig. 3 is sold under many different trade names. All of the variations are light-weight and most appear to provide a reasonable quality (stereoscopic) image. But there is one big problem: the instrument is focusing on its own object table. Normally it cannot be used to focus on the ground below.

Fig. 3: A small and cheap minimalistic portable dissecting microscope. 20fold magnification. LED battery incident light (cold light). The focusing mechanism is based on some kind of toothed wheel gliding over a rubber plate. This is definitely not ZEISS grade but in most cases it will suffice for focusing under outside conditions. But please note not that the instrument as delivered is not able to focus through its table onto the ground. It must be modified for our tardigrade application.

(4) A small DIY re-design will help to overcome our base-plate focusing problem:

Fig. 4: Same instrument as above, but DIY optimized for in situ ground investigation. With a little bit of drilling and re-screwing (or re-glueing) the black rubber focusing mechanism plate can be fixed in a lower position. As a conseqence the instrument will be able to much focus lower, onto the ground level. Overall this is an ideal instrument for our purposes: 20fold magnification, big working distance (which means that its optics will not become wet in use) - it can be placed directly on the moss surface. And, last but not least, it has a big field of view and an appropriate 20fold magnification.

After this mod we were actually able to study live tardigrades in their natural environment outside. This was a really thrilling naturalist's experience! We will show some image impressions in the next issue.

See you!

© Text, images and video clips by  Martin Mach  (webmaster@baertierchen.de).
The Water Bear web base is a licensed and revised version of the German language monthly magazine  Bärtierchen-Journal . Style and grammar amendments by native speakers are warmly welcomed.

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