Composting In Schools

Observing Compost Invertebrates

by Elaina Olynciw


In outdoor compost piles, a wide range of invertebrates take part in the decompostion of organic matter. Try monitoring invertebrate life in the pile over the course of the compost process. How long is it before you locate the first invertebrates? What happens to them when the pile heats up? Do you find different organisms later on, after the pile cools down?

In indoor container composting you may find fewer (or no) invertebrates, and decomposition is accomplished by microbes alone.



One method of collecting invertebrates is to take grab samples of compost from various locations in the heap. Some organisms such as centipedes and sowbugs will be more likely to be found near the surface. Others will be found deeper in the heap. Spread each compost sample in a large tray or pan, preferably light in color for maximum contrast. Students should use wooden tongue depressors, plastic spoons, or other instruments that will not hurt the organisms, to sort through the compost. Flashlights and magnifying lenses can be used to enhance the observation. The larger organisms, such as worms, centipedes, millipedes, sowbugs, earwigs, spiders, ants, beetles, snails, slugs, some mites, etc., can be observed with the naked eye. To get a closer look, place samples of the compost in petri dishes or watch glasses and observe them under a dissecting microscope.

An alternative method of separating small arthropods in compost is by using a "Berlese funnel". This method will provide a higher concentration of arthropods to view. Place a funnel with a 10-30 cm upper diameter in a ring stand. Attach a circle of 10mm wire mesh (hardware cloth) or window screen 8 cm below the funnel. Just below the funnel, place a vial to collect the specimens. Position a light source (25 watt) 2.0 - 2.5 cm above the funnel, or place the collecting apparatus in a sunny location. The light and heat drive the negatively phototaxic compost organisms downward through the funnel and into the collecting jar. If you use too strong a light source, the organisms will dry up and die before making it through the funnel.

Place compost in the funnel and then partially fill the vial with water if you want to observe live organisms. Observe the organisms about 2 to 4 days later. They will remain alive and float on top of the water. You can place them in a petri dish or watch glass and observe them under a dissecting microscope or with a magnifying glass. You should find small arthropods, including many different kinds of mites, a few different insect larvae, springtails, small millipedes, ants, etc.

The organisms can be lifted out with a paint brush and maintained in small chambers of plaster of paris (mixed with powdered charcoal to aid observation). This substrate must be kept continually moist to keep the arthropods alive. Adding brewer's yeast to the substrate provides a food supply for many species.

A mixture of 90% percent ethanol and 10% glycerol can be used to collect the arthropods if preserved organisms are needed for quantitative study. A grid of 1.0cm squares can be set up on a petri dish for counting. Removal of organisms can be accomplished with an angled sewing needle that has been filed flat. The pointed end can be imbedded in a cork or wooden dowel or matchstick. Thin, drawn out pipettes can also be used and rinsed out with alcohol if organisms get stuck.



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Department of Crop and Soil Sciences
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