E. Earth and Space Systems · Soils in the Environment

Living Things in Soil and Healthy Soil

E2.1 A1.1 A1.2 A1.4About 40 minutes

Learning goals

I can name living things found in soil, including ones too small to see.
I can explain how soil living things help soil, like decomposers making humus.
I can sort the parts of soil into living and non-living.
I can describe what healthy soil is like.

Words to know

organism
Any living thing: a plant, an animal, a fungus or a tiny living thing too small to see.

decomposer
A living thing that breaks down dead plants and animals, like worms, fungi and bacteria.

bacteria
Very tiny living things. You need a microscope to see them. Many live in soil and help break down dead things.

fungi
Living things like mushrooms and moulds. Many have thin threads that spread through the soil.

burrow
A hole or tunnel in the ground that an animal digs to live in.

healthy soil
Soil that is full of life, has humus and air spaces, holds water but lets extra water drain, and helps plants grow well.

A city under your feet

If you could shrink down to the size of an ant and crawl into the soil, you would find a busy underground city! There are tunnels, rooms, roots like giant pillars, and creatures everywhere.

Last lesson you learned about the non-living parts of soil. Today you will meet the living parts.

Remember from Grade 2

In Grade 2 you learned that an earthworm has no legs. It squeezes and stretches its body to move. You also learned that earthworms help make soil rich. Today you'll find out how.

Who lives in soil?

Plant roots. Roots are a living part of the plant that grows down into the soil.
Animals you can see: earthworms, ants, beetles, sowbugs and pill bugs, millipedes, centipedes, spiders, slugs, snails and grubs (baby beetles).
Animals that dig burrows: groundhogs, chipmunks, moles and some mice live in tunnels underground.
Fungi. A mushroom is only a small part of a fungus. Under the ground, the fungus has long, thin threads spreading through the soil.
Tiny living things too small to see, like bacteria. A spoonful of healthy soil holds millions of them, more than you could ever count!

An earthworm and a grey sowbug in dark, moist soil among thin plant roots and dead leaves. — An earthworm and a sowbug are two of the many living things in soil. Notice the plant roots too: they are a living part of soil. AI-generated image

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Some living things you might find in soil: 3 earthworms, 4 ants, 1 snail and 2 mushrooms (the parts of fungi we can see).

Soil living things have jobs

Decomposers (earthworms, sowbugs, millipedes, fungi and bacteria) eat dead leaves, plants and animals and break them down. This makes humus and puts nutrients back into the soil for plants. Without decomposers, dead leaves would pile up forever!
Diggers (earthworms, ants, moles) make tunnels. Tunnels let air and water move into the soil, and they mix the soil.
Earthworms leave behind droppings called castings. Castings are full of nutrients, like a gift of plant food.
Roots hold soil together, so it does not blow or wash away. When roots die, they decompose and add humus too.
Many fungi threads wrap around plant roots and help the plant get water and nutrients.

Even that lovely earthy smell after rain is made by tiny bacteria in the soil!

The busy city under your feet. Decomposers eat dead leaves, diggers make tunnels for air and water, and roots hold the soil together.

Worked example

Let's sort: living or non-living?

Sort these soil parts: earthworm, pebble, root, sand, mushroom, water, ant, air, dead leaf.

Ask: "Is it alive now? Does it grow, need food and water, and make more of its own kind?"
Living: earthworm, root, mushroom, ant. They grow and need food and water.
Non-living: pebble, sand, water, air. They were never alive.
The dead leaf is tricky. It was once alive, but it is not alive now. It is non-living (once living). Soon it will become humus.

Living: earthworm, root, mushroom, ant. Non-living: pebble, sand, water, air, dead leaf (once living).

What is healthy soil like?

Farmers and gardeners want healthy soil, because healthy soil grows healthy plants. Here is a checklist:

It is often dark in colour, because it has lots of humus.
It is crumbly. It breaks into small lumps with spaces between them, not hard like a brick.
It smells earthy, not sour or like chemicals.
It has lots of living things. Finding earthworms is a great sign!
Water soaks in after rain, and extra water drains away. It does not stay in puddles for days, and it does not run off the top.
It has air spaces for roots to breathe.
It has no garbage or harmful chemicals.
Plants grow well in it.

Healthy soil	Unhealthy soil
dark and crumbly	pale, hard and packed, or dusty and loose
many worms and other living things	few or no living things
water soaks in	water puddles on top or runs off
smells earthy	may smell sour or of chemicals
plants grow well	plants grow poorly or not at all

Comparing healthy and unhealthy soil

Worked example

Let's compare two soils

Leo and his mom test two places. Garden bed: dark and crumbly, 6 worms in one shovelful, a cup of water soaks in quickly. Path beside the swings: hard and pale, 0 worms, a cup of water makes a puddle. Which soil is healthier? Use evidence.

Look at the checklist. Dark and crumbly is a sign of humus. The garden bed has it. The path does not.
Living things: the garden bed has 6 worms, the path has 0. 6 − 0 = 6 more worms in the garden bed.
Water: it soaks into the garden bed, but it puddles on the path. The path has hardly any air spaces.
Every piece of evidence points to the same soil.

The garden bed is healthier. It is dark and crumbly, has more worms, and lets water soak in. The path soil is packed down by many feet.

Be kind to soil creatures

Look, but be gentle. If you lift a rock or log to peek underneath, put it back the way it was, so the animals keep their home. Don't pick up centipedes, spiders or beetles: some can pinch or bite. If you hold a worm, keep your hands wet and put it back on damp soil in the shade.

Just for fun

An earthworm has no legs, no eyes and no lungs. It breathes through its damp skin. Talk about an unusual way to take a breath!

Hands-on activity

Soil safari

You need: gloves, a small shovel or big spoon, a white tray or an old pillowcase, a magnifying glass (if you have one), paper and pencil.

With a grown-up, pick a spot: a garden bed, under a log, or under a pile of fallen leaves.
Scoop a few spoonfuls of soil and leaf litter onto the tray.
Gently spread it out. Look closely for 5 minutes. Make a tally chart of every living thing you find: worms, ants, sowbugs, beetles, millipedes, spiders, roots, fungus threads.
Draw your favourite creature and label it. Is it a decomposer, a digger or both?
Try a second spot, like the edge of a path. Which spot had more living things? What does that tell you about the soil?
Put the soil and creatures back where you found them. Wash your hands.

Research question (if you want more): With a grown-up, use a library book or a website to find out one more fact about your favourite soil creature.

Your turn

Name three living things that live in soil.

What is a decomposer? Give one example.

How do earthworm tunnels help soil?

Is a dead leaf living or non-living?

Give two signs of healthy soil.

Why are bacteria hard to find in soil, even though there are millions?

What should you do after you lift a log to look for creatures?

More practice: warm-up

Living or non-living: a root?

Living or non-living: a pebble?

Name one animal that digs a burrow in the soil.

What do we call the part of a fungus that pops up above the ground?

True or false: Finding earthworms is a good sign for soil.

More practice: on your own

What would happen in a forest if there were no decomposers?

Why are worm castings good for plants?

Soil in a playground is hard and pale, and rain makes puddles on it. Is it healthy? Give two reasons.

How do plant roots help soil, both while the plant is alive and after it dies?

Mia found 12 sowbugs under a log and 4 under a rock. How many more were under the log? Why might the log have more?

Challenge

Mushrooms, earthworms and bacteria look very different. What job do they share in soil?

Leo says, "Soil with no living things is just as good for plants." Do you agree? Use two facts to explain.

Plan a fair test: Which spot has more soil animals, under leaf litter or on bare ground? What will you keep the same?

Check your understanding

Quiz

Which of these is a decomposer?

Which list has only living things?

Earthworm tunnels help soil by...

Which is a sign of healthy soil?

A dead leaf in the soil is...

Why are bacteria important in soil?

For parents and teachers

Big idea (E2.1, living part and healthy soil): Soil is alive. Roots, fungi, bacteria, earthworms and many small animals break down organic matter, cycle nutrients, and build the crumbly, porous structure of healthy soil. Healthy soil is typically dark, crumbly, earthy-smelling, full of life, absorbs water and drains well.

How to help: The soil safari is a great 15-minute outdoor job. Encourage tally charts and comparison of two spots: that is real data collection (A1.2). A library book or reliable website for one extra fact builds research skills (A1.1).

Common difficulties:

Thinking all soil creatures are "bugs" or pests. Most are helpers. Worms, sowbugs and millipedes are not insects.
Living vs. once living. Dead leaves, humus and logs are non-living now but were once alive.

Interesting fact for adults: Most earthworms in Ontario today are not native. Glaciers removed earlier worm populations, and many species arrived with European settlers. In gardens they help, but in some forests they eat the leaf layer too quickly. You don't need to teach this, but it is a good answer if your child asks "Were worms always here?"

Safety (A1.4): Gloves, no picking up centipedes, spiders or beetles, return creatures and logs, wash hands.