Soil experiment: Summon the worms!

In this practical activity, your class will examine the importance of earthworms in breaking down organic matter to produce soil which helps plants to grow.

You'll go looking for earthworms by using mustard water to bring them to the surface of bare soil. The class can compare the number of worms found in different locations and discuss what this means for soil quality.

  • Key Stage: KS2 Year 3 (ages 7-8)
  • Time required: Activity 20-30 minutes (set-up, 5 minutes). Post-activity discussion can last longer.
  • Video transcript

    We’re here in the Natural History Museum’s Wildlife Garden and it’s spring, it’s damp in the soil, it’s really mild it’s the perfect day to go and look for earthworms.

    People think there is just one species of earthworm but that’s really not true. Even in the UK we have 27 different earthworm species and they can be really, really different.

    So in your compost bin for example, you get these fantastic stripy worms. We call them the tiger worms and they are hard at work breaking down all your compost like your old apple cores, any of the fruit and veggies. They break them down and produce absolutely fantastic fertiliser for your garden.

    Then if you head to your lawn and have a dig if you are allowed to - but if your not allowed to then maybe use some mustard water. Just Colman's mustard [1 large tablespoon of mustard powder in 1.5 litres of water] or if you don’t have that some washing up liquid dissolved in a bottle of water. Pour that on your lawn and just wait patiently and then earthworms will come up.

    You can find bright green worms. You can find black headed worms, grey worms, bluey-grey worms. Even I had a look in my garden this morning and found a fantastic specimen. This is the biggest earthworm you will find in the UK, Lumbricus terrestris – you can see it has a deep red head there, a really, really fine specimen!

    This would be a horrible planet to live on without earthworms. They are decomposing all the dead organic matter on the surface. They are bringing all this organic matter down into the soils making them rich and fertile. They are also aerating the soils. They are converting the nutrients in the soils to a form that plants can uptake more readily.

    Also people don’t think about the fact that they are they are vital in the food chain. So many different animals actually rely on earthworms as a source of food. So they are hugely, hugely important animals for all of us. And yet people don’t really give them a second thought! So start giving a bit more love to the humble earthworm!

About this resource

  • Resource type: practical outdoors, scientific reasoning, discussion based on results
  • Theme: Rocks and Minerals (National Curriculum Year 3)

Learning outcomes

  • Understand that some soils are formed of organic matter
  • Recognise the importance of earthworms in improving soil quality for plants

Running the activity

1. Watch the video above. Afterwards, discuss with your class that earthworms eat organic matter (the dead parts of plants and animals) such as leaves and food waste. This provides nutrients in the soil that plants can use to grow. For more in-depth information see the background science section below.

2. Practical: go looking for earthworms.

  • Following the video instructions, mix water with mustard or washing up liquid (1 large tablespoon of mustard per 1.5 litre bottle of water).
  • Have groups of students pour on patches of soil in different locations. Give a name for each location and keep track of how many worms appear after a couple of minutes.
  • Once finshed, wash off the worms and the sample area with clean water. If possible, put the worms back under cover in nearby soil  so they don’t get accidentally stepped on or eaten.

3. Once eveyone has collected the data, return to the classroom and display/present it to the whole class. Discuss why earthworms may prefer some soil types to others. Questions to dicuss:

  • Which soil locations had a lot of earthworms in them?
  • Which locations only had a few?
  • Why might there be different numbers at different locations?
  • What might earthworms like in a particular soil? (easy to move in, not too rocky, wetter so they don’t dry out, organic matter to eat)
  • Based on the number of earthworms found, which location might you expect to see more plants in?
  • How might earthworms (unintentionally) help plants?

The key to successful discussion here is the scientific reasoning behind responses. Even if suggestions may not seem ‘correct’ if they are well reasoned with evidence from this experiment this should be considered successful.

See extension activities below for further ways to explore this topic.

Materials required

  • Bottles/containers for the mustard water mixtures
  • A tablespoon of mustard for each container
  • Water
  • Gloves and goggles if handling soil or earthworms
  • Outside locations with bare soil where you can hunt for earthworms
  • Tubs to contain the earthworms briefly for counting

Background science

Soil is made up of smaller pieces of rocks and minerals as well as organic matter. Microscopic organisms, fungi and animals play a part in breaking down organic matter which then appears in soil. 

The ‘quality’ of soil for plant growth relies on nutrients within it as well as space for air and water to move through.

Earthworms bring down and consume organic matter such as leaf litter and their waste (worm castings) provides the nutrients in soil.  

Earthworms groupings include: Surface-Feeding, ‘epigeic’ (in leaf litter compost, Soil-Feeding, ‘endogeic’ (horizontally burrowing, often pale coloured), Composter (similar to surface feeding, likes warmth) and finally Deep-Living, ‘anecic’ (large, dark reddish brown).  

The relative acidity/alkalinity of the soil plays a big part in worm comfort. At lower KS2 it is not expected to be taught but if so desired it can be brought up in relation to appropriate real world experiences children may have at this age. E.g. the taste of vinegar or lemons for acids (humans don’t have specific alkaline taste receptors).

Earthworms have both male and female reproductive organs but some still need a mate to reproduce and lay eggs. The first segment of an earthworm (the peristomium) contains its mouth, the very last segment (the periproct) contains its anus.

Since Emma presented the video above, there are now 29 identified earthworm species in the UK.

Suggested extension activities and differentiation

Useful words
Learners at year three level may benefit from a simple word bank of relevant terms and unusual plurals: Earthworm, Soil, Plant, Leaf/Leaves. The term ’organic’ (being made of parts of living or once living things) may need to explained to all learners.

No mustard?
Instead of using mustard water it is possible to encourage worms to the surface through repetitive stepping on the soil. This does not need to be too heavy footed and can be done by younger children to the required effect. Alternatively a fork can be pushed into the ground and ‘twanged’ to make vibrations in the nearby soil.

School compost
How could we humans help worms and plants? Consider collecting food waste from school lunches and start (or add to an existing) compost bin. This has the bonus of helping humans dispose of waste sustainably too!

  • Curriculum links

Related activities

Practical observation: What's in soil?

In this practical activity, your class will get up close and see what they can find inside different soils, using samples from your own area.

Helpful resources

External Sites