Lessons · Living things
How many legs?
Spiders have eight and beetles have six, which means a log with four spiders on it is a times table nobody had to invent.
When
April to October
Outside
About 40 minutes
What it teaches
Skip counting and the beginning of multiplication, with a reason to do it.
What is going on
Six legs or eight is not a coincidence and not a rule someone made up. Insects are built from three body sections with one pair of legs on each part of the middle one; spiders are built from two sections with four pairs on the front one. The count is the body plan, which is why it never varies and why it is the fastest way to sort what you find under a stone. Millipedes and centipedes are neither, and have neither a thousand nor a hundred — they add segments as they grow, so an old one has more legs than a young one of the same species, which children find outrageous and then never forget.
What to look for
- Body sections. Three means insect, two means spider, and you can see it with the naked eye on anything bigger than a grain of rice
- Where the legs attach. All six insect legs come off the middle section, never the tail end
- Which way it runs when the stone comes up — towards dark, or down into the soil
- Woodlice: fourteen legs, and not an insect at all. They are crustaceans, closer to a crab than to a beetle, and they breathe through gills
Before you go
Everything goes back under the same stone the same way up. Nothing comes indoors. Wash hands afterwards, and leave anything that stings alone — looking is the whole lesson.
First, outside
What to do
What to take
- A hand lens if you have one
- A pale cloth or a sheet of paper to look at things on
- 1
Roll a log or lift a flat stone — then put it back the way it was, which matters more than anything found under it.
- 2
Count the legs on one thing. Really count them: it is harder than it sounds and the answer is almost always six or eight.
- 3
Sort what you find into the six-legged and the eight-legged. That is the actual difference between an insect and a spider, and a four-year-old can see it.
- 4
Now count two of the same thing. Then three. Write the running total in the dirt.
Out loud
What to say to each of them
All three at once, off the same bucket of acorns. Read down the column that matches the child in front of you.
2
Point and name
- “Look — legs! Lots of legs. Can you wiggle your fingers like that?”
- “How many legs have you got? Two. Count them: one, two.”
- “Gently. We look with our eyes and one finger.”
Subitising — seeing that a group is two without counting it — and the idea that a number word belongs to a thing you are touching.
4
Count and compare
- “Count the legs on this beetle. Point at each one as you say the number.”
- “Six legs. Now here is another beetle — how many legs on both of them?”
- “Spiders have eight. Is eight more than six, or less?”
One-to-one correspondence: one number word per object, the last word you said is how many there were. Then more, fewer, and the same.
6
Tally and figure
- “Four spiders. Eight legs each. Count in eights: eight, sixteen…”
- “If you found forty-eight legs and they were all beetles, how many beetles was that?”
- “Which is more — three spiders or four beetles? Work out both before you answer.”
Grouping as a way of counting past what fingers hold, and subtraction as the distance between two numbers rather than a taking-away.
When it is not working
What going wrong looks like
Most of what looks like failing is a child standing at a known place on a known ladder. Knowing which place changes what you do next, and it is usually not more practice.
About 2
Wants to hold it. Redirect to a finger's distance and a big cloth to look at things on. The rule that everything goes back under the same stone the same way up matters more today than any number.
About 4
Counts eight on a beetle. They are counting antennae, or counting a leg twice as it moves. Put it on a pale cloth where it will sit still for a second, and count from the front.
About 6
Adds four eights by writing 8+8+8+8 and counting on fingers. That is fine and correct — but show them counting in eights once. The point is not that adding is wrong, it is that there is a faster road.
How you know it landed
They sort a new find into six-legged or eight-legged before being asked what it is. Body plan before name is how a naturalist actually looks.
Rungs of the ladder this builds
Then, five minutes on screen
The same idea, drilled
The multiplication on its own, without the wriggling.
Why this order
The walk first, the game after. Reversed, the walk becomes the price of the game, and a child who has learned that outside is what you do before the screen has learned the wrong thing very efficiently.
If they want more
Millipedes and centipedes do not have a thousand or a hundred. Count the segments instead and multiply by two.
When you have done it
Ticking it keeps it off the next season plan, and nothing else.
We look, we count and we put it back. Nothing goes in a mouth — not a berry, not a mushroom, not a leaf. That is the whole rule, and it is the same rule every time.
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