Constructing a Baermann Funnel for Collecting Soil
Baermann funnels are a standard means for extracting nematodes from soils, and are easy to construct and use. The figure below shows one typical design. A small funnel is used to hold a soil sample with nematodes, and water is added to the funnel until the soil is just saturated. Nematodes will gradually move downward and sink to the bottom of the Baermann funnel.
; Small plastic funnel (e.g., 10 – 15 cm diameter)
; A ring stand or other way to hold the funnel
; Flexible surgical tubing (ca. 10 cm in length) that can be attached to the neck of the
funnel and clamped shut.
; A medium mesh screen, cut to fit the upper part of the funnel (ca. 6 cm diameter)
; Kimwipes, milk filters, paper towel, or facial tissue for holding wet soil samples
; Soil samples (ca. 25 g)
; Beaker of water
; Test tube, petri dish, or other collection vessel
; Pasteur pipette and bulb for collecting the nematodes
; Large petri dish with water agar (2% agar)
; Dissecting and compound microscopes
Methods (See figure below)
1. Construct the Baermann funnels as shown below. Place the tissue paper on the screen in
the top of the funnel. The tissue paper will be porous enough for nematodes to move
through, but fine enough to hold wet soil. Laboratory Kimwipes work great.
2. Weigh ? - 1 cup of soil (ca. 25 g) and carefully place on the tissue paper in the funnel.
Soil with abundant organic matter works best (forest, old field, grass, riparian).
3. Clamp off the tubing at the bottom and carefully add water to the funnel until the soil is
just saturated. The soil must always be in contact with the water. The top of the funnel
can be covered with plastic wrap or a petri dish lid to prevent the soil from drying out.
4. Leave undisturbed for 1-3 days; the nematodes will collect at the bottom of the tubing.
5. Carefully release about 1 ml of water with nematodes onto a water-agar plate; Alternately,
release a small amount of water onto a petri dish to examine the nematodes. The water
agar plates work best because, once the water evaporates, the nematodes are easy to count
and examine. Bacteria-feeding nematodes thrive on the water-agar plates that will also
contain lots of bacteria. It is also easier to pick up the nematodes from the agar surface.
Protozoa will also be visible.
Activities with Nematodes
Determine the effect of habitats or soil types on nematode populations
Calculate the rate of increase of nematodes in soils or on agar plates
Observe reproduction in nematodes
Observe nematodes feeding on bacteria (nematodes are translucent) and their internal structures are clearly visible)