Designing and making a choice chamber

As woodlice are found under logs and in leaf litter, a reasonable proposal is that they prefer being in the dark rather than light. To test this proposal, make a simple choice chamber from a round biscuit tin, or empty ice-cream tub, with a diameter of about 20 cm.

Line the tin with smooth brown paper stuck down with a glue stick, sealing the edges with sticky tape.

Divide the choice chamber into a light and a dark part, by covering half of it with, say, a table place mat.

Stick thick cardboard to the edge of the mat with sticky tape, and fold over at right angles to form a dark enclosure in the tin.

Cut the cardboard so it fits the inside wall of the tin closely. Trim the bottom edge of the cardboard to one centimetre above the bottom of the tin, giving woodlice free access to the light and dark halves.

Illuminate the choice chamber with a table lamp fitted with an energy saver light bulb (to avoid exposing the woodlice to heat).

Place ten woodlice in the choice chamber at time zero, and count the number of animals in the light half after ten minutes.

Subtract the number in the light half from ten to obtain the number in the dark half. During the ten minutes watch the behaviour of the woodlice, and write down your observations in a notebook.

* Are they running away directly from the direction of the light source in a straight line towards the dark?
* Or are they scurrying around in random directions, making turns until they happen to reach the preferred half where they remain?


Design of choice chamber for testing light vs dark


We tried this experiment with 70 pill bugs (Armadillidium vulgare), collected from damp shady spots underneath a loose log heap. The animals were divided into groups of ten. Each group of ten was placed randomly in the choice chamber and the position of each animal recorded at the end of the ten minutes. At the end of each ten minutes the group of pill bugs was replaced by a new group. The counts of the total numbers of pill bugs in each of the light and dark halves came to 35 for each at the end of the experiment. So there was no evidence that pill bugs prefer either light or dark. Try the same experiment with woodlice collected from a dry area; the results could be different.

The design of the choice chamber can be adapted to test woodlice preference for dryness or humidity. Cover the bottom of the dry half with about one cm depth oven-dried compost, or sand. The bottom of the humid side is covered with one cm depth of damp compost or sand. The humid side of the choice chamber is covered with a transparent polythene sheet with a curtain of polythene blocking off the humid from the dry side with a one cm gap allowing free entry and exit of woodlice.


Choice chamber for testing dry vs humid atmosphere.

Place each group of ten woodlice randomly in the choice chamber and note their behaviour. Record the position of each animal at the end of each ten minute period.

When you have finished your investigations, set your woodlice free, back where they were collected.

The importance of life in a log pile

Why are we so interested in the invertebrates living in log piles? Their feeding habits recycle nutrients essential for plant growth, and they provide food for frogs, toads, moles and badgers, so overall the diversity of life is increased. Log piles provide reservoirs of beneficial invertebrates that prey on pests such as slugs and millipedes.

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