Science 7–10 · Year 7

Leaf litter invertebrates: Tullgren funnel extraction and a dichotomous key

Science understanding: Biological sciences

Practical, model not builtLow risk

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The idea

Organisms are classified by shared structural features, and a dichotomous key turns those features into a repeatable series of either-or choices that ends in a named group.

Safety card

Low riskAn adult supervises

Hazards

Hot lamp globe and the fire risk of a lamp left over dry litter
Bites or stings from spiders, centipedes and ants
Soil microorganisms on hands

Controls

Lamp fixed in a stand at least 10 cm above the mesh, on a heat-resistant tray, and switched off whenever the room is unattended
Handle animals with brushes and forceps only; anyone with a known allergy handles trays only
Wash hands after sorting
Ethanol, if used, is kept away from the lamp

Note

No hazardous chemicals; record a RiskAssess risk assessment for the activity as school procedure requires.

What you need

Leaf litter, two 2 L bags per group (4 L in all), one scooped from a shaded, moist garden bed or under trees and one from a sunny, dry bed (with permission), each in a labelled bag
Tullgren (Berlese) funnel, one per bag and so two per group: a 20 cm plastic funnel resting in a ring stand, a disc of 2 mm mesh or flywire inside it, and a collecting jar beneath
Desk lamp with a 25 W incandescent or halogen globe, one per funnel, held 10 to 15 cm above the litter (the method relies on heat from the globe drying the litter from the top)
Collecting jar for each funnel, with 2 cm of damp paper towel for live release, or 20 mL of 70 % ethanol if specimens are to be kept
White sorting trays, fine paintbrushes, soft forceps, x10 hand lenses and a stereo microscope
Printed Australian Museum leaf litter invertebrate dichotomous key, one per pair
Data table with columns for group (order or class), tally, and habitat

How to do it

Collect one 2 L bag of litter from a shaded bed and one from a sunny, dry bed; note the site, date and depth of litter at each.
Set up one funnel per sample. Spread the litter on the mesh, place the collecting jar under the funnel stem and position the lamp 10 to 15 cm above the litter.
Leave each funnel under its lamp for 24 h of lamp time, spread over two or three school days if the lamp is switched off whenever the room is unattended. Heat and drying drive the animals down through the mesh into the jar.
Tip the jar contents into a white tray with a little water or ethanol. Use brushes, not fingers, to separate animals.
Work through the dichotomous key for each animal under the hand lens or stereo microscope, answering each couplet from a visible structural feature (number of legs, body segments, wings, antennae).
Tally each animal against its group. Photograph any animal you cannot key out and check it later against Atlas of Living Australia records for your area.
Three groups sample each habitat, so the class holds three bags and three counts per habitat; pool the class counts and compare the mean number of animals and the number of groups found per bag.
Return live animals to the site they came from.

What you should see

A bag of moist shaded litter usually yields many small animals, commonly dominated by mites (Acari) and springtails (Collembola), both groups on the Australian Museum key, with ants, beetles, slaters and spiders among the larger finds; the dry sunny litter is expected to yield fewer animals and fewer groups, which the class's three bags per habitat test. The learner knows the key worked when two people keying the same animal reach the same group, and when every couplet was answered from a feature they could see rather than a guess.

What changes

What you change: Litter habitat (shaded and moist versus sunny and dry)
What you measure: Number of invertebrates and number of groups per 2 L bag
What you keep the same: Volume of litter per bag (2 L)
Extraction time (24 h of lamp time)
Lamp wattage and height above the mesh
Mesh size (2 mm)

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

All small crawling animals are insects; spiders (eight legs), millipedes and slaters are not.
Organisms are grouped by where they live or how big they are, rather than by structure.
A key identifies to species; the Australian Museum leaf litter key stops at broad groups such as mites, spiders, beetles and slaters, which is what its couplets can support.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Science 7–10 Syllabus (2023)SC4-CLS-01 SC4-WS-01 SC4-WS-05
Australian Curriculum v9AC9S7U01AC9S7I03AC9S7I04

Sources

The pages the author read to write this activity.

All Concept Studio activities