Constructing Berlese Funnels to Study Invertebrate Density and Biodiversity
Easy, inexpensive, authentic, and engaging—what better way to study biodiversity and population density than to construct and use Berlese funnels?
In the 1880s Antonio Berlese, an Italian entomologist, built a system to remove small invertebrates from soil samples. His first design was large and much more complex than the system that you will make, but it worked in much the same way. A soil sample is placed into a funnel positioned over a container of alcohol. Heat is used to desiccate the sample from above. As the soil begins to dry, small invertebrates in the sample move downward, eventually falling into the container of alcohol where they die and are preserved. These invertebrates can then be studied.
Here are instructions for making a Berlese funnel, followed by some ideas for how to use the funnel in various classroom activities.
Materials (Needed for each Berlese funnel)
- 1-Gallon Plastic Jug (e.g., milk jug)
- Jar (e.g., 1-qt canning jar)
- Mesh Screen (1/4” hardware cloth)
- Ethanol (70–95%) or Isopropanol (70%)
- Lamp with Moveable Neck (and incandescent bulb, for heat)
- Collected Soil Sample
- Using scissors, cut the bottom off the jug.
- Pour 2 cm of alcohol into the jar.
- Place the milk jug funnel’s spout in the mouth of the jar. The jug serves as the funnel. The jar is the collection chamber.
- Bend the mesh screen so that it fits securely into the milk jug and forms a stable platform for the soil sample. Do not let the screen fall below the handle.
- After introducing a soil sample into the funnel and placing the funnel on the jar, tape a ruler or similar support to the handle of the funnel and to the side of the jar to ensure that the funnel remains steady.
- Adjust the lamp to direct the light onto the top of the sample from about 20 cm away.
The following suggested activities are appropriate for high school students and address the following National Science Education Standards for grades 9–12:
Science as Inquiry
- Abilities necessary to do scientific inquiry
- Interdependence of organisms
- Matter, energy, and organization in living systems
Basic use of the Berlese funnel
Have students work in teams to collect samples from areas with a variety of ground covers (e.g., leaf litter, grass, humus, compost, mulch). Each team measures a 15 × 15-cm sampling plot and then uses their hands or a trowel to collect the soil in their plot to a depth of 5 cm. Teams place their samples into a bucket or plastic bag and transport the soil back to the lab.
To load the funnel, remove it from the jar and hold it over a bucket or paper towel while the class carefully pours or scoops the sample into it. (This prevents any loose debris from falling into the alcohol.) Once the sample has settled in the funnel such that debris has stopped falling, replace the funnel on the jar and secure it with a ruler and tape.
Place the Berlese funnel where it will not be disturbed for 5–7 days. Position a lamp with an adjustable neck over the sample, about 20 cm away, to aid in the drying process. As the sample continues to desiccate, small invertebrates accumulate in the alcohol. After 5 days, or when the sample is completely dry, remove the funnel and cap the jar. Then, with stereomicroscopes, examine the specimens. For diversity studies, you may wish to provide a dichotomous key of local soil invertebrates.
Set up several Berlese funnels. Have students collect a variety of soil samples to analyze separately, comparing density and diversity data. Some ideas for comparisons include the following:
- Samples collected in sunny areas versus those from shaded areas
- Samples exposed to pesticides or fertilizers versus those not exposed
- Samples with varying pH
- Samples from moist areas versus those from dry areas
- Samples from disturbed sites (e.g., compost piles, gardens) versus those from undisturbed sites
- Samples collected from the same site during different seasons
Students may choose to compare total invertebrate density, or they may choose a specific, common, local soil invertebrate and compare its density between sites. After collecting data, students can use several calculations to compare density and/or diversity data between sites.
Number of invertebrates in the sample/Area of the sample site = Density per 225 cm2 (assuming 15 × 15 cm). Students can convert this figure to density per square meter for each site.
Several calculations can be used to compare diversity between sites, including the Jaccard Index, Sorensen Quotient of Similarity, Mountford Index of Similarity, Simpson Index of Diversity, and Shannon-Weaver Index. Choosing which to use may depend on the data, the textbook you are using, or your own preference. It may be instructive to discuss the subtleties in the applicability of the various indices.