Dichotomous Key Worksheet Generator
Draws three to ten invented creatures — round or long bodies, legs or none, wings, antennae, spots, tails and shells — and builds a numbered key of yes/no couplets that leads to each creature's name. The drawings are lettered in a shuffled order so the key does not give the answers away, and you can leave one or two couplets blank for pupils to complete. Before the sheet appears, the key is walked for every creature to prove it reaches that creature and no other.
What this generator does
Makes the skill of following a dichotomous key practisable as often as needed, with creatures nobody can look up: each sheet has new creatures and a new key, and the answer page gives the couplet path to each name (1 no → 2 yes → 4 no).
How to use this tool
- Choose how many creatures, 3 to 10.
- Tick the box to leave gaps in the printed key if pupils should finish it themselves.
- Press Make a key puzzle, read the status line for the check, and print: drawings and key on page one, answers on page two.
Understanding the controls
- How many creatures
- 3 to 10; each needs its own end, so more creatures means a longer key.
- Leave gaps
- Blanks one or two couplets on the printed key for pupils to complete.
- Paper and seed
- Paper size and density for printing; a seed rebuilds the same sheet while the generator is unchanged.
Worked examples
- Seed 'pond', six creatures
- A five-couplet key: 1a Body long … go to 2; 1b Body round … go to 4; 2a Has wings … Norrow; 2b No wings … go to 3; 3a Body spotted … Pindle; 3b Body plain … Wuzzle; 4a Has a tail … Klunk; 4b No tail … go to 5; 5a Has wings … Vorple; 5b No wings … Quib. Quib's path is 1 no → 4 no → 5 no.
- Six creatures with gaps
- The last couplet and the middle one are printed as blanks; the answer page repeats the complete key.
Common use cases
- Practising a key before using a real one on leaf or invertebrate samples
- Writing couplets: the gaps make pupils choose a feature that splits a group
- A quick classification starter
How this generator works
Each creature gets a random combination of eight visible features, with no two creatures alike. The key asks, at each step, the question that splits the remaining group most evenly, so a key for n creatures has exactly n − 1 couplets. A separate check walks the finished key for every creature, confirms it ends at that creature's name, and confirms every couplet splits its group into two non-empty parts.
Randomness and fairness
Creatures, names and drawing order are drawn with the browser's cryptographically secure generator, or from one seeded draw when a seed is typed. Seeded sheets are deterministic, not cryptographic. The key is built deterministically from the creatures.
For how randomness is produced across the whole site, see how Generate Random works.
Limitations and good to know
- The creatures and names are invented for practice. Real keys use features that need a hand lens or expert judgement; these use features that are obvious in a drawing.
- The key always splits the group as evenly as it can. Published keys are often uneven on purpose, following natural groups; this one teaches the method, not a classification.
- The drawings are simple monochrome outlines; tiny print densities can make spots and antennae hard to see.
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