Publication Extract

The following extract is the Teachers notes page about woodlice, from the BES Publication, "Food Chains and Food Webs"

INVESTIGATION 2: What do woodlice like to eat?

Aim

The aim of this investigation is to introduce the children to the recycling of materials in nature and to highlight the importance of decomposer organisms, such as woodlice, in this process.

Time of year

Any, although late summer and autumn are best, as there are plenty of leaves to provide material for investigation and this season could be a useful context for highlighting the significance of decomposers.

Safety issues

If children are outside collecting woodlice or eathworms, work must be carried out in accordance with LEA/school guidelines. Sites unlikely to have been contaminated with dog faeces should be chosen. Teachers should check for broken glass, etc. Ensure that children wash their hands after handling soil, etc.

Animal welfare issues

Cultivate sensitivity to living organisms. Handle woodlice and earthworms with care. Do not use forceps; careful fingers or an artist's paintbrush are best. Keep animals in optimum conditions and return them to their original habitats after the investigation.

Resources

Woodlice. These are commonly found under stones and logs where there are damp crevices in which they can hide.'Bug pots' or margarine tubs are suitable containers for collecting the animals. All stones and logs should be replaced after searching. The woodlice used for the investigation should all be similar in appearance (i.e. likely to be the same species). Do not mix the kind which roll up with those that do not.
To keep woodlice for just one or two days, a lining of moist paper towel in the bottom of a container will suffice. If they are kept longer, a layer of soil with some bark pieces and leaf litter will be required. Ensure that the soil and atmosphere are moist but not wet and that the animals are kept in a cool place.
A variety of possible foods for the woodlice, such as fresh leaves of different plants, dead and decomposing leaves, tree bark, flower petals. Chose material you can cut or break into areas of known size e.g. 1 cm²
Small containers with lids e.g. petri dishes, margarine tubs
Filter paper or paper towel
Graph paper, pencils, Sellotape, scissors, marker pens and notebooks
Water
Paintbrushes for handling woodlice; tweezers for handling food items

Background

Woodlice are excellent organisms for study. In some parts of the UK they are called slaters or sow bugs. They are not insects, but belong to the group Crustacea, which includes crabs, shrimps and lobsters. The adults have seven pairs of legs. They can be found almost anywhere in large numbers and are relatively easy to keep in the classroom. In times gone by, woodlice were carried in a small pouch around the neck and swallowed as a remedy for stomach aches and other ailments!

Food chain connections

In their natural environment, woodlice have an extremely important role. They feed mainly on decaying material, helping to break it down and return the nutrients to the soil. Woodlice are therefore decomposers. They provide a source of food for a variety of carnivorous animals, one of their main predators being centipedes.

Introducing the activity

Explain to the children that in nature nothing is wasted. The materials of life are recycled and used again and again. This is due to the action of certain animals and other organisms, such as fungi, called decomposers. Woodlice are very important animals, as they are often the first link in recycling dead plant remains. It is the children's task to find out the types of food woodlice prefer to eat in their natural environment.

Procedure

The children should work in pairs.
Line the bottom of the petri dishes or margarine tubs with moist filter paper or paper towel. Each food substance to be tested is cut into pieces 1 cm x 1 cm and placed in the petri dish or tub. For a standard size petri dish or tub, use three or four types of food and put two squares of each into the container. Get the children to think about the positioning of the squares: should the duplicate squares be placed next to each other or some distance away? The term 'fair test' could be introduced here. Mark the positions of each type of food on the lid.
Gently introduce two woodlice into each container, secure the lid and leave for two days. Woodlice are nocturnal, so find a cool, dark place for the container.
Examine the containers and return the woodlice gently to their classroom home or to the place where they were collected. If the children collected the woodlice themselves, it is a good idea to see that they return them to the underneath of the same rock or log.
Using tweezers, remove the squares of 'food' and dry them on paper. Then stick them with Sellotape over a 1 cm x 1 cm square marked on graph paper and estimate the area of food that has been consumed by counting the number of small squares visible (i.e. how much leaf material has been removed from the original square). The children can then decide which is the favoured food of the woodlice and relate it to their role in recycling organic matter. We have also found that there is usually a copious amount of woodlouse faeces, which children like to stick in their notebooks too!

Handling results

Tabulate individual and class results.
Make individual and class bar charts.
Enter class data onto a spreadsheet and print out bar charts.

Conclusions can be drawn about the implications of the results for the recycling of materials in nature: woodlice prefer some foods to others so the preferred foods are likely to be broken down more quickly than others. Some decomposers are responsible for the breakdown of animal bodies. Many small dead animals are buried by burying beetles, which then lay their eggs near the corpse. When the eggs hatch, the larvae feed on the body.

Try to relate the classroom experiments to real life situations and work covered elsewhere in the curriculum. One child in our trials concluded that the woodlice preferred leaves to eat, so must be able to climb trees! We had made the assumption that children knew that leaves of many trees fall to the ground in autumn. (But of: course woodlice are able to climb trees!)

Follow-up work

Further investigations using woodlice

The investigation could be refined in a variety of ways. If the children have identified that woodlice feed primarily on dead leaves, you could suggest that the leaves of some species might be more readily broken down by woodlice than others are. One tried and tested investigation shows that when woodlice are offered leaf squares of oak, ash, sycamore and beech they have distinct preferences. They prefer to eat leaves high in nutrients e.g. ash and sycamore. Leaves such as oak and beech have a lower nitrogen content but are rich in tannins and waxes, making them unpalatable and less favoured. However, if you leave woodlice long enough they will eat everything, including the paper towel or filter paper!

Investigating the diet of earthworms

Similar experiments to those described previously could be carried out with litter feeding earthworms. Earthworms also form a very important decomposer link in many food chains. They can be kept in the classroom in a wormery or even in plastic pots filled with soil. Different types of food can be placed on the surface of the soil and the worms will selectively pull down their preferred food into the soil. Be sure to collect earthworms for this exercise from the surface litter layer and not from deeper in the soil, where worms are more likely to be soil feeders. The favoured food of litter feeding earthworms is, of course, fallen leaves, though they show distinct preferences. Ash, elm and poplar are all favoured and for this reason persist on the ground only for a few weeks after falling. Oak and beech leaves are not liked and remain on the ground for many months. Sycamore leaves are moderately acceptable. These points illustrate the importance of decomposers in recycling organic material and returning it to the soil.

Links with Design and Technology

Get the children to observe woodlice in their natural surroundings, record the typical features of their habitat, then design a home for woodlice which simulates their natural environment and requirements (i.e. dark, moist allowing air to circulate etc.).

A petri dish containing woodlice and food items.

Make sure that the food items are labelled. If the labels are on the lid, put marks on it and on the bottom part of the dish to enable you to line up the labels and the food items properly