Day 2: Worm Worlds
Compare the number of earthworms living in different parts of a study area by forcing worms to the surface using a non-lethal irritant (hot mustard slurry!). Youngsters try to explain differences based on environmental conditions they can observe - soil conditions, ground cover and local physical conditions.
For each team of 2 or 3 youngsters:
- 1 Quarter Square Meter Quadrat (See Equipment Card)
- 2 Mustard Slurry Jugs (See Equipment Card)
- 1 white basin, pan or bowl - 6" min. size (for holding worms)
- 1 pair of scissors or grass clippers (for clipping grass to see worms better)
- 1 pencil to record data
- 1 copy of the Action Card
- 1 Record Sheet on cardboard or clipboard
For the whole group:
- 1 extra jug with 2 gallon of water (for wetting basins and rinsing worms)
- 1 Data Board and marker, or blackboard and chalk (for summing up the whole group=s findings)
Site. Survey the area a few days before going out with youngsters. Do a couple of trials with the mustard slurry to get an idea of how many earthworms your youngsters might find. Make sure there are at least two types of habitat in your study area for comparison of worm numbers, e.g., planted beds versus lawns, playing fields versus ornamental lawns, heavily trampled versus untrampled lawns, or plant beds with wood chips versus leaf mulch groundcover. Locate a convenient water tap, e.g., an outdoor spigot, where the Mustard Slurry Jugs can be filled just prior to use.
Time of year. This investigation works best when worms are active, that is, when soils are warm and moist. Frozen or exceedingly dry conditions should be avoided.
- Gather the whole group and show them the general study area. Spark their interest by telling them there are lots of worms here.
- Tell the youngsters they will be counting the numbers of worms in two parts of the study area and comparing worm numbers and the environment in the different habitats. Have the youngsters look around the area and list the different types of below-ground places or habitats they see and note that these all are potential worm habitats.
- After they've named 3 or 4 habitats, have them agree on 2 to compare as worm habitat. Help them come up with a reasonable comparison, such as healthy grass versus heavily trampled grass, or bare soil in the open versus under shrubs.
- Divide the group into teams of 2-3. Tell each team they will sample worms in each of the 2 habitats. Outline the boundaries of the 2 habitat types.
- Show the teams how to set up the quadrat and how to sample earthworms (see Action Card). Distribute materials (1 set/team), set a time for getting back together and then, let the teams go.
- Allow each team to select their own sampling sites, but stress the need for all teams to follow the same procedures so that their results will be comparable.
- Circulate among the teams, helping them pick places to sample (random is best), set up their quadrats and sample worms. Things to look out for:
Crooked quadrats (samples won=t be comparable).
Pouring slurry too fast (slurry runs out of quadrat, fewer worms are sampled).
Injured worms (unnecessary harm).
Too much grass or litter layer (can=t see worms - remove surface grass and litter).
No observations made of environmental conditions (coax youngsters to fill in their Record Sheet).
No worms (this could lead to interesting comparisons or hypotheses)
- Call the teams together at the appointed time. MAKE SURE THAT THEY'VE CLEANED UP:
Worms are returned to the quadrat or an adjacent spot (not in direct sunlight).
Water jugs are rinsed and left to air dry.
Quadrat twine is wrapped carefully around stakes and stored properly.
- Have each team fill in its findings-worm numbers and environmental conditions for the two habitats-on the Summary Chart. Then, calculate the mean (average) number of worms (both total and just juveniles) per quarter square meter and compare the two habitats.
- Display the Data Board so all the teams can see it.
- Which habitat had the most worms? The most juvenile worms? Why do you think this was so?
- In what ways did the environmental conditions in the two habitats differ? Which differences do you think might explain the differences you found in worm numbers?
- Did each team find the same number of worms within each habitat? If not, why do you think worm numbers differed?
- Now that you know how to sample earthworms, the sky's the limit for the questions you might ask about these fascinating creatures. What would you like to find out next?
MORE WORM WONDERINGS
Here are some nice data display and math extensions to try back inside:
- Convert your results to the number of worms per square meter (m2) by multiplying the number per quadrat by 4. This gives you an estimate of worm population density in worms per m2, units that most worm scientists use and are familiar with (see graph).
- Graph your results. For example, use bar graphs of worm numbers or the percentage of juvenile worms in your two habitats.
- Estimate the total number of worms in one of the habitats in the study area:
Determine the area (in m2) of the habitat by measuring its perimeter (e.g., for a rectangular area, multiply length x width).
Multiply this area by the mean worm population density for the habitat to get the estimated number of worms in the entire area.
BETTER WORM WORLDS?
Discuss with the youngsters how they might improve part of the study area as worm habitat. What changes would they make? How would they test whether their actions worked?
For more information about worms, here are some useful resources:
1. Earthworms, a Teacher’s Guide. Great Explorations in Math and Science (GEMS) - Lawrence Hall of Science, Berkeley, CA.
2. Compost Critters. Bianca Lavies. 1993. Dutton Publishing, New York, NY.
3. Wonderful Worms. Linda Glaser. 1992. Millbrooke Press, Brookfield, CT.
4. Earthworms, Dirt and Rotten Leaves. Molly McLaughlin. 1986. Avon Books, New York, NY.
- Worm Worlds complete lesson plan (pdf, 1 MB)