Pill Bug Behaviour Experiment: A Choice Chamber

Ten pill bugs go into the middle of the chamber. One half is damp, the other is dry, and every thirty seconds your child counts how many are on each side. After ten minutes the tally is lopsided: maybe sixteen damp-side observations out of twenty. That is a pill bug behaviour experiment producing genuine behavioural data, the kind that appears in journals, in a tub from the recycling. And because these are living animals, the twenty-minute time limit, the shade, and the release at exactly the spot you found them are not optional extras. They are the experiment.

Key Takeaways

• Ten pill bugs in a two-sided chamber, one half damp and one half dry, counted every 30 seconds for 10 minutes.
• It teaches animal behaviour and, more precisely, the difference between a kinesis and a taxis, which most school resources get wrong.
• Fits ages 7 to 13. The counting discipline is the hard part, not the setup.
• The usual failure: no control run. Without a both-sides-damp trial you cannot rule out a side preference.
• Hard limits: 20 to 30 minutes total, in shade, no lamp, then released where they were collected. Same day.

What You’ll Need

Item	How much	Where to get it	If you don’t have it
Pill bugs	10	Under a damp log, flowerpot, brick or paving slab	Sow bugs (the flatter ones that don’t roll up) work and behave similarly
Shallow plastic container with lid	1, about 20 × 15 cm	Food container from the recycling	Two yoghurt tubs joined by a short cardboard tube
Paper towel	2 sheets	Kitchen	Plain brown paper; avoid printed newspaper
Water	a tablespoon	Tap	—
Soft paintbrush	1	Craft drawer	A leaf or a folded card to scoop with. Never pinch them with fingers
Small ventilated pot with soil from the collection site	1	Yoghurt pot with pinholes in the lid	Any container with air holes and damp leaf litter
Timer	1	Phone	Clock with a second hand
Paper and pencil	1 sheet	School supplies	A tally needs to be fast; use paper

Time: collection 15 min, experiment 20 min, release 5 min Cost: nothing Mess level: low, but there will be soil on the table

Do the Experiment: The Pill Bug Behaviour Experiment

Step 1 — Collect gently, and note exactly where

Lift a damp log or flowerpot and look underneath. Scoop ten animals with a soft brush or a leaf into the ventilated pot with a handful of soil and leaf litter from the same place. Mark the collection spot, a photograph works, because that is where they go back. Keep the pot in shade from this moment on.

Step 2 — Build the chamber

Line one half of the container with damp paper towel, wrung out so it is moist but not puddled, and the other half with dry paper towel. Leave a 1 cm gap between them so the moisture doesn’t wick across. Put the lid on loosely, or use a lid with air holes.

Step 3 — Run the control first

Before the real trial, line both halves with damp paper and run the full protocol for five minutes. If the animals pile up on one side anyway, you have a side bias (a draught, a light gradient, a slope), and you need to fix it before the real run means anything. This step is what separates an experiment from a demonstration.

Step 4 — Take a prediction, then start

Ask: “Which side will they end up on, and how strongly?” Get a number, not just a side: “fifteen out of twenty”. Then place all ten animals in the centre line, cover, and wait two full minutes without counting. That settling period lets the disturbance of being moved wear off.

Step 5 — Count every 30 seconds for 10 minutes

At each 30-second mark, record how many animals are on the damp side. Twenty observations. Count what you see at that instant; don’t wait for stragglers or tidy up ambiguous cases — if one is halfway across, record it as the side its head is on and be consistent.

Step 6 — Release them, then do the maths

Put every animal back under the same log, with the soil you borrowed, within half an hour of collecting them. Then add up: total damp-side counts divided by 200 possible animal-observations gives the proportion of time spent on the damp side. Compare it to the control run.

What you should see: rapid, fairly frantic movement for the first minute or two, then a clear accumulation on the damp side — typically 70 to 90 percent of observations. They will also clump together, often in a pile in a corner of the damp half. A few individuals will stay on the dry side the whole time, and that variability is real data rather than noise to be hidden. Expect some to roll into balls when handled; they unroll within a minute if left alone.

What’s Actually Going On

Pill bugs are not insects. They are terrestrial isopods, crustaceans more closely related to crabs and shrimp than to beetles, and their ancestors were aquatic. That history explains everything you are about to observe. They breathe through structures on their abdominal appendages, pleopodal lungs, which only work when moist, and their cuticle lacks the waxy waterproofing that lets an insect survive dry air. A pill bug in a dry room loses water fast and suffocates slowly.

So they end up in damp places. But here is the part almost every school resource gets wrong: they do not navigate toward moisture. Pill bugs have no mechanism for sensing which direction is damper and steering that way. What they have is a change in movement pattern depending on local conditions. In dry air they move faster and turn less often; in damp air they slow down and turn more, and often stop. Behaviour that changes speed or turning rate in response to a stimulus, without directional orientation, is a kinesis. Steering toward or away from a stimulus is a taxis. This is a kinesis, and the accumulation in the damp half is a statistical consequence of the animals wandering randomly but lingering where conditions are good.

Gunn’s 1937 study of the humidity reactions of the woodlouse Porcellio scaber in the Journal of Experimental Biology is the classic work establishing this, and Warburg’s 1964 paper on isopod responses to temperature, humidity and light extended it across conditions and species. The distinction matters because it is the same logic that explains how bacteria find food, how some larvae find shade, and why “the animal wants to be there” is often the wrong explanation for where animals are.

The clumping is its own adaptation, not just crowding. Broly, Deneubourg and Devigne’s analysis of aggregation in woodlice argues that grouping reduces water loss per individual by cutting the exposed surface area, and treats this as a factor in how isopods managed to colonise land at all. So your pile in the corner is doing two things at once: it has found the damp half, and it has made the damp half damper.

One last identification note, because children care about it. Pill bugs in the genus Armadillidium roll into a tight ball, conglobation, when disturbed. Sow bugs, usually Porcellio or Oniscus, are flatter, have two small tail projections, and run rather than roll. Both work for this experiment, and comparing their behaviour side by side makes a better investigation than using one.

How to Explain It to Your Kid

Ages 5–8: They breathe like a fish out of water

Tell them these animals are relatives of crabs who moved onto land but never finished the job. They still breathe with gills that only work when they’re wet, so in a dry place they can’t breathe properly. That’s why the damp side fills up.

Then give them the counting job, with you keeping time. Counting ten animals twenty times is a lot of counting for a seven-year-old and it is genuinely useful work. Finish with the release, and make it a ceremony: same log, same soil, say goodbye. The returning matters as much as the result.

Ages 9–12: Kinesis versus taxis, and a proportion

Introduce both words and the difference. Then ask the question that tests it: if a pill bug could sense which way was damper, what would you expect to see in the first thirty seconds? A direct march. Instead you see random-looking wandering that gradually concentrates. That observation is the evidence for kinesis.

Then compute the proportion: damp-side counts over 200, as a decimal and a percentage. Compare with the control. If the control gave 50 percent and the test gave 85 percent, they have a result. Ask them how confident they are and why, with ten animals.

Ages 13+: Design it properly, and take the ethics seriously

With a teenager, this becomes a real study design problem. Variables to consider: number of animals, trial duration, observation interval, order of control and test, whether the same animals are reused, and side bias. Have them write a protocol before touching anything, then follow it exactly.

Then the ethics, explicitly. The Association for the Study of Animal Behaviour and Animal Behavior Society guidelines for the treatment of animals in behavioural research and teaching, published annually in Animal Behaviour, set out the principles that apply here: use the minimum number of animals, minimise harm and distress, and return animals to their habitat where possible. A fourteen-year-old can read that framework and apply it to their own protocol, which is a genuinely grown-up thing to do.

The question to ask: “If pill bugs don’t steer toward damp, how did they all still end up on the damp side? Could you end up somewhere without ever choosing to go there?”

Why Teaching This Early Pays Off

Most primary-school biology is description: what animals look like, what they eat, where they live. This is the rarer thing, an experiment on behaviour with a quantitative outcome, and it introduces a style of reasoning, statistical accumulation from undirected movement, that is genuinely hard and genuinely important.

It also sets up the kinesis/taxis distinction before biology makes it abstract. Plant tropisms, bacterial chemotaxis and animal orientation all appear in later curricula, and a child who has watched an undirected mechanism produce a directed-looking outcome has the right intuition already loaded. Our piece on biomimicry and engineering problems picks up the same thread: simple local rules producing useful global behaviour is how swarm robots work too.

And it teaches research ethics by doing rather than lecturing. A child who agreed to a twenty-minute limit and kept it, who used a brush rather than fingers, and who walked the animals back to their log, has practised something that most people only encounter as a form to sign. The honest caveat is the usual one: nothing about an afternoon with woodlice predicts academic outcomes, and no study claims it does. What it leaves is one real dataset, one hard concept, and a demonstrated habit of caring about the subjects of your experiment. For the observational habit that goes with it, see nature journalling with families.

Before You Start: What Parents Should Know

Best age	7 to 13. Below seven, the 30-second counting discipline collapses and handling tends to be too rough.
Supervision	Adult present throughout, enforcing the time limit, the shade, and gentle handling. The adult does the release if the child won’t.
Real hazards	None to the child — pill bugs do not bite or sting. The risk is to the animals: heat, drying out, being squeezed, or not being released. Wash hands after handling soil.
Don’t	Don’t use a lamp as a light source — the heat kills them. Don’t keep them longer than half an hour. Don’t collect from anywhere that may have been treated with pesticide or slug pellets. Don’t let a child under five handle them at all, and never put them in water.

Four specifics that matter. No lamps: a desk lamp over a small container raises the temperature fast, and these animals have no defence against drying. Thirty minutes maximum from collection to release, and if anything delays you, release them and try again another day. Release at the collection point, not somewhere similar — local moisture and their own aggregations are there. And handle with a brush or a leaf, never by pinching: their exoskeleton protects against predators, not against a child’s grip.

When It Doesn’t Work

• They won’t settle and keep running laps. They are still reacting to being moved, or the chamber is too bright. Extend the settling period to three minutes, put the lid on, and move everything into deeper shade.
• Half of them are rolled into balls and not moving. Handling stress. Leave them completely alone for two minutes; they unroll. If they don’t, they’ve had enough — release them and run it again another day with gentler collection.
• The counts are 50/50 with no preference. Check the damp side is actually damp and the dry side actually dry. Wrung-out paper towel in a humid room dries out within minutes; re-dampen and restart. Also check the gap between halves is wide enough that moisture isn’t wicking across.
• The control run shows a side preference. Good catch, and that’s the point of running it. Find the asymmetry: a draught from a window, light from one side, a table that isn’t level. Fix it, re-run the control, then do the test.
• You can’t find any pill bugs. They are under things, in damp shade, often against the underside of a brick or the rim of a flowerpot. Water a shady patch the evening before and look in the morning. A compost heap edge is reliable.

Take It Further

Change the variable, keep the protocol. Run light versus dark with both halves equally damp, by covering one half with card. Then run rough versus smooth substrate. Each run needs its own control. Build a small table of proportions across all three variables and rank them: which stimulus produces the strongest accumulation? That ranking is a real finding about what matters most to the animal.

Measure the mechanism, not just the outcome. Instead of counting positions, film one animal for two minutes on damp paper and two on dry, and count how many times it turns in each. If the kinesis explanation is right, turning rate should be higher on damp paper and speed lower. Measuring the proposed mechanism directly, rather than only its consequence, is the step that turns a school activity into science.

What to Watch For Over the Next 3 Months

• Week 4: They look under things. Logs, stones, plant pots — and they report what they find rather than just poking it.
• Month 2: The word “crustacean” is used correctly and with slight indignation at anyone who says “bug”.
• Month 3: They propose a controlled version of something unrelated (a plant, a pet, a sibling’s reaction time) and remember to include a control. That is the transfer worth having.

Frequently Asked Questions

Are pill bugs safe for children to handle?

Yes. They have no bite, no sting and no venom, and they are not known to carry disease relevant to humans. The safety concern runs the other way: they are easily crushed, dried out or overheated. Handle with a soft brush or a leaf, keep them in shade, and wash hands after touching soil.

How long can we keep them?

Half an hour, start to finish, and then straight back under the log they came from. They lose water quickly, they live in established aggregations, and a container is a poor substitute for a damp microhabitat. If you want to keep woodlice longer term, that’s a different project requiring a proper enclosure, not this one.

Are they insects?

No. They are terrestrial isopods — crustaceans, with fourteen legs as adults, related to crabs and shrimp. They breathe through modified gill-like structures that must stay moist, which is the whole reason this experiment works. Insects have six legs and waterproof waxy cuticles.

Why do they go to the damp side if they can’t sense direction?

Because their movement pattern changes with local humidity. In dry conditions they move faster and turn less; in damp conditions they slow and turn more, and often stop. Random wandering plus “linger where it’s damp” accumulates them in the damp half without any steering. That is a kinesis, not a taxis.

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About the author

Ricky Flores is the founder of HiWave Makers and an electrical engineer with 15+ years of experience building consumer technology at Apple, Samsung, and Texas Instruments. He writes about how kids learn to build, think, and create in a tech-saturated world. Read more at hiwavemakers.com.

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Sources

1. Gunn, D. L. (1937). “The Humidity Reactions of the Wood-Louse, Porcellio scaber (Latreille).” Journal of Experimental Biology, 14, 178–186. https://doi.org/10.1242/jeb.14.2.178
2. Warburg, M. R. (1964). “The response of isopods towards temperature, humidity and light.” Animal Behaviour, 12, 175–186. https://doi.org/10.1016/0003-3472(64)90119-8
3. Broly, P., Deneubourg, J.-L., & Devigne, C. (2013). “Benefits of aggregation in woodlice: a factor in the terrestrialization process?” Insectes Sociaux, 60, 419–435. https://doi.org/10.1007/s00040-013-0313-7
4. Association for the Study of Animal Behaviour / Animal Behavior Society. (2020). “Guidelines for the treatment of animals in behavioural research and teaching.” Animal Behaviour, 159, I–XI. https://doi.org/10.1016/j.anbehav.2019.11.002
5. National Research Council. (2012). A Framework for K-12 Science Education. National Academies Press. https://doi.org/10.17226/13165
6. Alfieri, L., Brooks, P. J., Aldrich, N. J., & Tenenbaum, H. R. (2011). “Does discovery-based instruction enhance learning?” Journal of Educational Psychology, 103, 1–18. https://doi.org/10.1037/a0021017