Worm food investigation

Created Date:
Thu 29 October 2020

Last Edit Date:
Fri 6 November 2020

Students build a mini worm farm and investigate the factors that affect the rate worms consume food including the size of the food (large/small) and type of food (hard/soft). The initial lesson and investigation set up will take about one hour, with ongoing observations (10 minutes) twice a week over three weeks, followed by another full lesson to discuss final observations.

Learning objective

Students observe changes in the mini worm farm and record their information in table format to show how the needs of the worms are met.

Curriculum links

Science: Science understanding

Biological sciences

Science as a human endeavour

Nature and development of science

Science: Science inquiry skills

Questioning and predicting
Planning and conducting
Evaluating

Cross-curriculum priority: Sustainability

Background information

Worm farms contain composting worms that eat food scraps and turn them into a natural liquid (worm leachate) and compost (castings) that can be used in the garden. Composting worms thrive in a moist, high nutrient environment and we create this environment in a worm farm.

Worm farms:

Decrease the amount of organic waste sent to landfill.
Close the recycling loop by changing food waste back into organic fertiliser for growing food.
Reduce greenhouse gases. In a well-maintained worm farm the decomposition process is aerobic (with oxygen), rather than anaerobic (without oxygen).

The earthworms used in worm farms are a different species to those we find in our garden. The best worms for worm farming are European worms such as the red wriggler (lumbricus rubellis) and the tiger worm (eisenia fetida). These species are accustomed to soils high in nutrients. They eat and breed much faster than other earthworms and can quickly transform food scraps into worm castings. They do this in a small amount of space, while other earthworms are better equipped for burrowing and searching for food in our drier, nutrient poor soils.

Worms are blind, but sensitive to light. Their instinct is to move away from light due to their two ‘photoreceptors’, which are sensitive nerve endings located near the saddle (Murphy, 2005).

Living conditions in a worm farm

Worm farms should be situated in a cool, shady spot. Worms need cool, moist conditions and a temperature of 25–26 degrees. They need a layer of bedding to live in, which can include castings, shredded paper, newspaper, cardboard, brown leaves, and straw. As food scraps decompose, they will make the worm bedding more and more acidic, therefore it is a good idea to occasionally add some garden lime to maintain the pH as worms prefer a neutral environment.

School worm farms

A worm farm is made from a container that has a drainage hole for water and a lid that keeps out vermin but allows air in.

You can buy worm farm containers, make your own, or have one custom made. Some schools use old bathtubs but most use old fridges that have been safely degassed. Look at the ‘How to build a worm farm’ fact sheet to find out more. For most schools, at least one large worm farm (such as a fridge or bathtub) is needed.

For information on what to feed a worm farm and what to keep out, see the ‘Waste wise worm farming’ and ‘How to make a fridge worm farm’ fact sheets: www.wasteauthority.wa.gov.au/wws/teaching-resources/list/fact-sheets

Resources required

A two litre clear plastic drink bottle per pair (with the top cut off, see diagram)

Moist worm castings

Compost worms

Large and small vegetable and fruit scraps

Hard and soft vegetable and fruit scraps (for example, carrots and a banana, pre-prepared for P–2 only) – chopped into similar sized long strips so that you can place them up against the edge of the bottle

Activity

Demonstrate the setup of a mini worm farm to the students. This activity could be carried out as a whole class, or students could work in pairs to create their own mini worm farm with one of the food types. Ensure that all the food types (large, small, hard, and soft) are included so that students can compare their farm with others containing different food types.

Investigation instructions

To make a mini worm farm, place about five centimetres of castings in each bottle and add a small handful of worms. Add about five centimetres more of castings.
Carefully dig a small hole right next to the side of the container and bury one type of food item (large, small, hard, or soft) in the bottle. Make sure that you can see the food through the side of the bottle and that the food is completely covered with castings.
Add a small amount of water to moisten the worm farm. Wrap the outside of the bottle with a piece of newspaper and place a damp newspaper ‘plug’ on top.

Predictions

Ask students to predict which food types they think will be broken down the fastest.

Observations

Check the mini worm farms every few days and add a little water if required. Represent and communicate observations in the following ways:
- Students orally compare observations of their worm farm with other students.
- Record observations on a chart as a class, and students write in their science journals. Use Table 1 as a guide to record observations (for example fruit is smaller, many worms around the fruit, fruit is gone and so on).
- Students can draw a picture of their worm farm on the first day, then again once each week. They could also take a photo.
Observations should continue until all the food scraps have been converted into castings.

Discussion

Discuss which food was eaten the quickest and compare with original predictions. Discuss what happens to the school food scraps when they go into the school worm farm and how worms turn organic matter into castings.
Discuss the questions: What living conditions do worms like? Why is the school worm farm a suitable place for worms to live?

Once the experiment is finished, return the worms to their regular home in the school worm farm.