The most rewarding thing I did this summer was help my friends, Stuart and Jeanette, build a very large compost bin. The bin was designed to look like the chicken coop, consume the year’s garden and kitchen waste and turn it into nutrient rich soil for the spring gardens. We love cooking, eating, gardening and enjoying the results of a day’s work with good friends. All the while, our busy composting friends are doing the same thing.
In small-scale outdoor composting systems, soil invertebrates contribute to the decomposition process. Together with bacteria, fungi, and other microbes, these organisms make up a complex food web with primary, secondary, and tertiary level consumers. The energy source is organic material and the result is organic matter.
Of all the components of soil, organic matter is probably the most important and most misunderstood. Organic matter serves as a reservoir of nutrients and water in the soil, aids in reducing compaction and surface crusting, and increases water infiltration into the soil.
Organic material and organic matter are different. Organic material is anything that was alive in or on the soil. For it to become organic matter, it must decompose into humus. Humus is organic material that has been converted by microorganisms to a resistant state of decomposition. Organic material is unstable in the soil, changing form and mass readily as it decomposes. As much as 90 percent of it disappears quickly because of decomposition.
Stable organic matter has been broken down until it is resistant to further decomposition. We are grateful to the invertebrates who make this happen.
Invertebrates of the Compost Pile
(organisms that eat secondary consumers)
centipedes, predatory mites, rove beetles, ants,carabid beetles
(organisms that eat primary consumers)
springtails, some types of mites, feather-winged beetles
nematodes, protozoa, rotifera, soil flatworms
(organisms that eat organic material)
bacteria, fungi, actinomycetes, nematodes, some types of mites, snails, slugs, earthworms, millipedes, sowbugs, whiteworms
leaves, grass clippings, other plant debris, food scraps, fecal matter and animal bodies including those of soil invertebrates
It all has to do with nitrogen conversion. The above consumers increase the surface area of organic material so that microbes can convert atmospheric nitrogen to a form of nitrogen that all living organisms can use.
In addition, these invertebrates are in constant motion, tunneling through the material which aerates the heap and allows water to enter. As each decomposer dies or excretes, more food is added to the web for other decomposers. Let’s meet these hardworking creatures.
Nematodes: These tiny, cylindrical, often transparent microscopic worms are the most abundant physical decomposers (a handful of decaying compost contains several million). Under a magnifying lens they resemble fine human hair. Some species scavenge on decaying vegetation, some feed on bacteria, fungi, protozoa and other nematodes, and some suck the juices of plant roots and root vegetables.
Mites: Mites are the second most common invertebrate found in compost. They have eight leg-like jointed appendages. Some can be seen with the naked eye and others are microscopic. Some hitch rides on the back of other faster moving invertebrates such as sowbugs, millipedes and beetles. Some scavenge on organic debris, while others eat fungi, and yet others feed on nematodes, eggs, insect larvae and other mites and springtails. They can be free-living or parasitic.
Springtails: Springtails are extremely numerous in compost. They are very small wingless insects distinguished by their ability to jump when disturbed. They run in and around the particles in the compost and have a small spring-like structure under the belly that catapults them into the air when the spring catch is triggered. They chew on decomposing plants, pollen, grains, and fungi. They also eat nematodes and droppings of other arthropods and then meticulously clean themselves after feeding.
Earthworms: Earthworms do the most decomposition work. They constantly tunnel and feed on dead plants and decaying insects. Their tunneling aerates the compost and enables water, nutrients and oxygen to filter down. As soil or organic matter is passed through an earthworm’s digestive system, it is broken up, neutralized by secretions of calcium carbonate from calciferous glands near the gizzard and finely ground prior to digestion. Digestive intestinal juices rich in hormones, enzymes, and other fermenting substances continue the breakdown process and pass out of the worm’s body in the form of casts. These casts are the finest quality of all humus.
Slugs and snails: Slugs and snails generally feed on living plant material but fresh garbage and plant debris in compost is also desirable.
Centipedes: Centipedes are fast moving predators found mostly in the top few inches of the compost heap. They have formidable claws behind their head which possess poison glands that paralyze small red worms, insect larvae, newly hatched earthworms, insects and spiders.
Millipedes: Slower and more cylindrical than centipedes, they have two pairs of appendages on each body segment. They feed mainly on decaying plant tissue but also eat insect carcasses and excrement.
Sow Bugs: Sow Bugs are fat bodied crustaceans with delicate plate-like gills along the lower surface of their abdomens that must be kept moist. They move slowly around the organic materials digesting as they go.
Beetles: Rove beetles, ground beetles and feather-winged beetles are most common. Elongated Rove beetles and rounder Ground beetles prey on other insects, snails, slugs and small animals.
Feather-winged beetles feed on fungal spores.
Ants: Ants feed on aphids, fungi, seeds, sweets, scraps, other insects and sometimes other ants. Compost provides some of these foods as well as shelter for nests and hills. By bringing fungi and other organisms into their nests, ants benefit the compost heap by moving minerals like phosphorus and potassium around.
Flies: During the early stages of the composting process, flies provide ideal airborne transportation for bacteria on their way to the pile. Flies spend their larval phase in compost as maggots, which do not survive thermophilic temperatures. Adults feed upon organic vegetation.
Spiders: Spiders feed on insects and other small invertebrates.
Pseudoscorpions: Pseudoscorpions are predators which seize victims with their visible front claws, then inject poison from glands located at the tips of the claws. Prey include minute nematode worms, mites, larvae, and small earthworms.
Earwigs: Earwigs are large predators, easily seen with the naked eye. They move about quickly. Some are predators. Others feed chiefly on decayed plants.
Cornell Composting and the Environmental Protection Agency http://compost.css.cornell.edu/invertebrates.html http://www2.epa.gov/students have extensive sites and tools for educating and engaging you in waste awareness.
How You Can Help:
- Build a compost bin! Get infinite joy using it!
- Ew! Who knew hummus was dead bugs and excrement! Look for these creatures and thankfully cheer them on so we can have more great soil.
- Inner cities have composting resources at green markets, farmers markets, and green spaces like neighborhood gardens.
- Learn about composting inside with earthworms.
- Engage in your community and reduce the amount of organic material that gets into the municipal solid waste stream.
- Learn what these amazing composting invertebrates can and cannot use to enrich your soil and continue the cycle forever. How cool is that?!
Until next week,