What it shows
A choice chamber lets worms pick between foods. The amount eaten of each food shows what to feed a vermicompost bin and what to avoid.
The science
Earthworms eat soft, partly rotted plant matter and avoid acidic or strongly smelling foods. By offering four foods at once, you can see their preference from how much of each is left. This helps you build a healthy vermicompost bin.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A shallow plastic tray divided into four sections with card
- Compost earthworms from a vermicompost bin
- Banana peel, tea leaves, dry leaves, citrus peel
- Damp soil or old compost
- A kitchen scale
- A damp cloth to cover
Safety
For this project: Wear gloves and wash hands after handling worms and soil. Handle worms gently and return them to their bin afterwards. Keep the tray away from food areas.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Divide the tray into four equal sections and fill each with damp soil.
Weigh 20 g of banana peel, tea leaves, dry leaves and citrus peel and place each in a different section.
Put ten earthworms in the centre where the four sections meet.
Cover with a damp cloth and keep the tray in a dark shaded place.
After one day, record the number of worms in each section.
After seven days, take out the leftover food and weigh it.
Calculate how much each food was eaten.
Draw a bar chart of mass eaten for each food.
What you should see
The bar chart shows which food the worms ate most and which they avoided, for example more banana peel and less citrus.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1What is a choice chamber?
A tray that offers several conditions so animals can choose.
2What do earthworms do to soil?
They loosen it and add nutrient-rich castings.
3Why avoid citrus in a worm bin?
It is acidic and irritates the worms.
4Why return the worms after?
They are living animals and useful for the garden.
Take it further
Test whether worms prefer chopped or whole food of the same kind.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
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