Macro-organisms in Composting
In our Compost Safari sessions for schools, we look at the larger creatures that live, or may be found, in the compost heap or bin. These creatures, sometimes known as Macro-organisms, physically break down the organic material by chewing, tearing and, in some cases, sucking it into smaller pieces and by eating and excreting material they make it more digestible for microorganisms (Compost Microbes) which also digest theirexcrement.
When looking for compost creatures it is usually more successful to use a cold compost bin as the hunting ground as the heat generated during the initial phases of hot composting does not make the hot bin a friendly environment for the creatures. Once a hot compost bin reaches the cool maturing stage it becomes more bug friendly
The creatures can be divided into three groups Primary, secondary and tertiary consumers based on what they eat. The primary consumers, mainly microorganisms ( ) eat the organic residues, the secondary consumers eat the primary consumers and the tertiary consumers eat the secondary.
Creatures that eat primary consumers
Creatures that eat secondary consumers
Includes microbes e.g.
bacteria, fungi, actinomycetes,
nematodes, mites, earthworms, fruit flies, millipedes, snails, slugs, woodlice (and pilbugs), white worms
rotifers, soil flatworms*
*For identification information on UK native and non-native flatworms go to
Many people worry about having ants in their compost heap but ants contribute to the composting process by bringing fungi, and other organisms, into their nests as well as introducing minerals e.g. phosphorus and potassium. Ants feed on a range of food including aphid honeydew (produced by aphids from t plant sap excreting), fungi, seeds, scraps and insects some of which are found in the compost heap. Compost provides some of these foods and it provides shelter for ants nests when cold composting techniques are being used or during the maturation stages of hot composting when the compost has cooled. Several species found in the UK including Lasius, Myrmica and Formica species
Beetles are insects with two pairs of wings. Types commonly found in compost include the:
- Rove beetle (staphylinids). There are 994 species of this large family of beetles living in the Britain. Adult rove and ground beetles prey on snails, slugs, and other small animals. Rove beetles are 2-30mm long, they are normally black or brown in colour, but some have red wing-cases and markings.
- Ground beetle (or carabids). There are 364 species of ground beetle living in the British Isles. Carabus violaceus has metallic-purple edges to the wing-cases and thorax. It is, 20-25mm long and feeds on slugs, leatherjackets and cutworms.
- Feather-winged beetles are the smallest beetles, usually a millimeter or less in length.
Featherwing beetles live in compost heaps and leaf-litter as well as other habitats containing moist organic materials which will support the growth of the molds and fungal spores upon they feed.
- Dung beetles. Some dung beetles can be found in compost heaps where they live on decomposing vegetation and on decaying fungi.
Centipedes and Cockroaches
These are normally found in the top layers of the compost heap. Centipedes are flat, segmented worms with one pair of legs in each segment. They are tertiary consumers that feed on soil invertebrates, small worms, insect larvae, newly hatched earthworms plus insects and spiders, which may reduce the populations in the compost bin.
he native species that may occasionally be found in the compost heap normally live in the leaf litter. They have relatively short legs and are slow in comparison with the introduced species. Cockroaches can eat relatively hard vegetable matter and have a symbiotic relationship to bacteria, hosting the bacteria in their body fat.
Some earthworm species live in accumulations of organic matter such as compost heaps. These include Eisenia fetida (brandling or tiger worm) and Dendrobaena veneta (These are the species most commonly used in wormeries).
Earthworms are the probably the most important of the physical decomposers in a compost heap. They eat organic matter, digest the bacteria on it, and excrete castings rich in nutrients such as calcium, nitrogen, magnesium and phosphorus. Their tunneling helps aerate the compost and their tunneling helps water, nutrients and oxygen to filter through the heap.
Earwigs are easily seen with the naked eye. Some species are predators while others feed on the decayed vegetation in the heap. Earwigs show a degree of parental care for their young protecting the nymphs, which look like smaller versions of the adult, from predators. Earwigs have characteristic pair of pincers on the abdomen and membranous wings folded underneath short forewings. The hindwings are said to resemble the human ear which might explain the name but many seem to prefer the old wives tail that earwigs burrowed into the brains of humans through the ear to lay their eggs .
orms are relatively small and live in the films of water around the composting materials. They are scavengers that eat a wide range of materials including animal matter. For identification information on UK, native and non-native, flatworms go to:
Flies are two-wing insects that feed on almost any kind of organic vegetation, detritus, including plant sap, blood, and other insects. Many types of flies, including black fungus gnats, fruit flies (see below), soldier flies, minute flies and houseflies can spend their larval phase in compost during the early stages of the composting process. However, the maggots will not survive thermophilic temperatures.
Fruit Flies and Fungus Gnats
Fruit flies are primary consumers during the composting process they are from one to two millimetres in size and they feed on the fruit acids. Their bodies are usually orange or light brown in colour and are their lower of their lower bodies have a bulbous shape. Fruit flies lay their eggs the adults lay their eggs on bananas and other fruits, which we buy. They can hatch while the fruit is in the house and when the skins are transferred to the compost bin or wormery, the flies develop. They can appear in a cloud of flies when the bin lid is removed. The flies are harmless but the cloud is often considered a nuisance. The numbers can be controlled by always keeping a layer of Browns e.g. shredded paper, cardboard or dry leaves on top of the heap. Food waste should be buried at least eight to twelve inches below the surface of the compost. Alternatively, the flies can be caught in a simple banana skin trap and released away from the bin or wormery or studied in the classroom. (see http://www.mass.gov/eea/agencies/massdep/recycle/reduce/how-to-control-fruit-flies-and-fungus-gnats.html)
Fungus gnats (sciarid flies) are small (about 1 mm) flies.They have black bodies which lack the bulbous shape of the fruit fly.The larvae are slender semi-transparent white maggots, up to 6mm long, with black heads. Their dark coloured gut contents may be visible to the naked eye or under a lens. The gnat larvae can damage indoor plants, seedlings and cuttings when contaminated compost is applied,
Millipedes have segmented bodies, with each segment, except the front few, having two pairs of legs that move in waves. Millipedes help break down plant material by eating the soft decaying vegetation as well as insect carcasses and excrement.
Mites are the second most common invertebrate to be found in compost. Some are visible to the naked eye while others are microscopic. They have eight leg-like jointed appendages. Some of the mites found in compost scavenge on leaves, other organic debris and fungi.
Fermentation mites, also called mould mites, are transparent-bodied creatures that feed on yeasts and soft plant material. They can survive in the anaerobic conditions of fermenting compost that can occur if the too many nitrogen rich “Greens” have been added to the bin.
Others species are predators feeding on nematodes, eggs, insect larvae, other mites and springtails.
Some of the mites that can be seen in compost are relatively fast moving and often light brown in colour. These tend to be predators.
Slower moving mites, often reddish brown in colour appear to be attracted to vegetables particularly those with a high water content cucumber, squash and melon http://www.redwormcomposting.com/worm-composting/a-mite-is-a-mite-is-a-mite-not-quite/ (If you are interested in Worm Composting I would recommend you sign up to this site which was created by Bentley Christie, creator of Compost Guy, and Worm Composting Canada)
The third group identified in Red Worm Composting are White Shiny Round Mites that can easily be mistaken for “worm eggs”. In fact, they are smaller than worm cocoons.
Nematodes (Roundworms) and Rotifers
Nematodes are cylindrical microscopic creatures usually less than 1mm long and are most abundant of the physical decomposers. Some resemble small white threads while others are transparent. Some live on decaying organic matter; others are predators of bacteria, fungal spores, protozoa and other nematodes.
Rotifers are minute worms that live in the water, which adheres to plant material in the compost bin where they feed on microorganisms. Their bodies are round and divisible into three parts: a head, trunk, and tail. They usually have one or two groups of vibrating cilia on the head.
Potworms and Protozoa
Pot worms (enchytraeids) are small-segmented white worms, growing to 10-25mm, which are found in large numbers in wormeries and compost heaps.
Adults measure about a quarter of an inch, and can literally appear to be in the millions in comparison to your red wiggler worm population. This species prefers a moist acid environment and feed mainly on fungi, decomposing vegetation, and bacterial.
It is said that potworms can be removed from compost, or caught for a demonstration, by adding a piece of bread soaked in milk, which will attract them and can removed taking the worms with it.
Protozoa are single-celled and microscopic organisms. They obtain their food from organic matter in much the same way bacteria they play a much smaller part in the composting process but because they are present in smaller numbers than bacteria.
Pseudoscorpions and Springtails
Pseudoscorpions are arachnids, between 2-8mm in size, that resemble miniature scorpions but without a tail or stinger. They hunt nematode worms, mites, larvae, small worms and other small invertebrates using smell and vibration, seizing the prey with their front claws before injecting them with poison.
Springtails (or Collembola) are tiny, less than 6 mm, wingless insects named because of their ability to jump. Most species have an abdominal, spring-like appendage that is folded beneath the body that is used for jumping. It is held under tension and it is released when the animal is threatened and strikes against the substrate, flinging the springtail up to 20cm into the air (and hopefully safety?). There are around 250 species in Britainand they tend to be very numerous in compost. They chew on decomposing plants, pollen, grains, and fungi. They also eat nematodes and droppings of other arthropods. then meticulously clean themselves after feeding.
Slugs and Snails
Snails and slugs. Are molluscs that travel in a creeping movement. Snails have a spiral shell with a distinct head and retractable foot. Slugs do not have a shell and are somewhat bullet shaped with antennae on their front section.
They feed primarily on living plant material, but they will also east mould and vegetable matter and plant debris in the compost heap.
Slugs vary in size from the grey field slug (Deroceras reticulatum), which is no more than 5cm (about 2in) long, to the large black slug (Arion ater), which can be 12cm (about 5in) when fully extended. Some slugs vary in colour; Arion ater can be black, orange-brown or buff coloured. Most slugs live in or on the soil, compost bin or wormery surface and remain active throughout the year, they are most active at night or in wet weather.
Snails are soft-bodied mollusks, with a hard shell, they can eat leaves, stems and flowers of many plants and are dormant during the autumn and winter. Damp warm increases their activity and they are most active at night and in wet weather.
The common garden snail, (Cornu aspersum) as its name implies is the species most frequently found in gardens. The Banded snails (Cepaea species), which are a little smaller and often brightly banded brown, white and yellow cam also be numerous
Spiders and Woodlice
Spiders are eight-legged creatures and third-level consumers that feed on insects and small invertebrates. Spiders are the largest order of arachnid, with over 40,000 classified species and numerous spiders can be found in the compost bin. As predators they have a role to play in helping to create balance in the compost bin by controlling the populations of other compost creatures that may slow the composting process, e.g. by eating Springtails which feed on and reduce the fungi which are Level. Web-building spiders can be found in the corners of the bin or inside the lid. While the free travelling Wolf spider is commonly found in the compost bin.
Woodlice (Sow bugs, pillbug, roly-poly, slaters potato bug) have a flat and oval body with distinct segments and ten pairs of legs. There are several species of woodlice commonly found in gardens and compost. They are usually grey in colour and up to 1cm long with the body segments sometimes flecked with yellow or pinkish brown markings. Some species, known as pillbugs, can roll themselves into a ball as a defensive mechanism.
They are first-level consumers that feed on rotting woody materials and other decaying vegetation.
Many kinds of worms, including earthworms, nematodes, red worms and potworms eat decaying vegetation and microbes and excrete organic compounds that enrich compost. Their tunneling aerates the compost, and their feeding increases the surface area of organic matter for upon which the microbes can act. As each decomposer dies or excretes, more food is added to web for other decomposers. Red worms are surface-dwelling worms These Epigeic species are poor burrowers and prefer to live and feed in the loose, surface and litter layers of soil they are found in the compost heap during the cooler phases and are traditionally used in wormeries
Other Wildlife : Frogs, Toads, Newts, Slow worms and Grass snakes
The compost heap or bin may also provide a temporary home to larger creatures. wildlife might appear in your compost heap.
Frogs, Toads and Newts may be occasional visitors or even use a compost heap for hibernating over winter so be careful when turning it.
Slow worms eat slugs so the bin may well provide a convenient lunch spot and if it is on the dry side a welcome home. If you find you have slow worms living, and breeding in the bin, do not disturbed them.
Grass snakes also be found in the compost heap and will occasionally lay eggs in the compost. If you find leathery white eggs in the compost start another bin or heap so as to avoid disturbing them at least until late summer.