Michael J.Roberts, the author of the excellent work on spiders "Spiders of Britain and Europe" describes his "Spi-pot"(it's not my idea) as follows:
To make a Spi-pot, you 'll require two clear plastic pots, a small piece of polystyrene sheet and a piece of clingfilm. I use pots with a 50mm diameter base, 67mm high, which originally contained glacé cherries or mixed peel. When stacked together there is a gap op 8mm between the bases.
The polystyrene sheet, 8mm thick, comes from packing or tiles. The base of one pot is cut out leaving a rim of 5mm for rigidity (pot A in the illustration). Place the second pot on the polystyrene sheet, draw around the base of the pot and cut out the circle of polystyrene with a sharp knife. Stick the polystyrene to the base with a PVC glue (pot B in the illustration).
Inclusion of a mm. scale on the polystyrene is very usefull for measuring the length of specimens in the field. This can be done with indian ink and a radiograph pen, ruling a scale line or a grid of mm. squares, or a piece of mm. square graph paper can be stuck on.
Finally, take a piece of clingfilm (about 25cm square) and stretch this tightly and evenly over the cut base of pot A, wrapping the surplus loosely around the sides. The captured spider is placed in pot A and trapped between the clingfilm and polystyrene when pot B is pushed in. Don't worry if the edge of the polystyrene is a bit ragged; parts of this will help grip, and parts will allow the passage of air when the cups are separated again.
The thickness of the polystyrene is not too critical, but it must reach up to the base of pot A. If you wish to examine the upper surface of the spider, hold the pot base up and trap the spider as it walks on the polystyrene. For a view of the under surface, hold the pot the other way up whilst manoeuvring. For a side view, fiddle around a bit and catch it unawares. Try to trap the spider in the centre of the pot. When examining male palps from the side, slightly compress the specimen once the palp is in clear view.
The clingfilm is very durable and very good optically when stretched tightly and evenly. When it becomes dirty, simply unravel and move on to another section.
The method of holding spi-pot and field microsope is illustrated. If you possess a field microscope, hours of (observation)fun are guaranteed...
If we want to work on a scientific base and before we go on to homebound determination, we'll have to note down some data (that you evt.can sent to me):
