Scientists once thought termite gut bacteria did the wood digesting. Purdue and Florida researchers fed colonies wood or paper and cataloged more than 4,500 species of bacteria. The bacteria did not change with the diet, while termite and protist gene activity did, so the bacteria seem to have little to do with digestion. In the hindgut of the termite Reticulitermes flavipes, the researchers counted over 4,761 species-level bacterial types, and diet-linked shifts were not statistically significant or the same across colonies. They suggest the environment, the founding pair, or the termites' genes may shape the mix. A single termite species can carry up to 12 kinds of protozoan symbionts along with hundreds of kinds of bacteria. In most termites the wood is not digested by the insect alone: protists, which are tiny one-celled living things in the gut, help turn it into food for the colony.
When termites and their gut protists were given woody, lignin-rich diets, about 500 genes changed their activity, and the lead scientist believes this may be important for breaking down lignin. Before termites bite, decay fungi in rotting wood have already broken cellulose into smaller pieces, so termites eat decayed wood faster than sound wood. They also eat the soft part of the wood grain first and leave the harder part. A termite colony has three main castes of workers, soldiers, and kings and queens, and termites eat wood in the wild. University of California experts add that termites break down woody debris, return nutrients to the soil, and tunnel in ways that keep soil porous and healthy enough to support plant growth.
Termites are eusocial: scientists use three traits, which are that adults care for the young together, some individuals are sterile and work for the colony, and two or more generations overlap in the colony. Trophallaxis is the passing of gut contents between nest mates. It shares food, and it hands the cellulose-digesting protozoans to young termites, which then have the microbes they need. In Colombian Amazon pastures, mounds of the soil-feeding termite Patawatermes turricola changed the soil. Researchers measured the mounds' physical and chemical differences from the soil around them.
A wood-stake experiment in boreal, temperate and tropical forests found that moisture is an important control of wood decay. Termites, however, changed decay rates in ways that climate alone cannot predict. Living animals may therefore predict wood decay better than climate in the tropics. Soil animals are still missing from many climate and carbon models. A 2026 review says they strongly shape how soil organic matter forms and turns over, yet are absent from nearly all existing frameworks that describe the cycles of elements. Tropical and temperate soil food webs also work differently. Tropical webs have more energy flow and rely more on living roots and predators, but less on bacteria, fungi and dead leaves, so there is a shift from a brown web to a green web.
Scientists measure how fast things rot with litterbags, which are leaf litter sealed in mesh bags and left on the forest floor. Bags with large holes let bigger animals in, so comparing bags shows how much of the breakdown the animals do. Litterbags use local leaves, so results are hard to compare between places. The Tea Bag Index fixes this: researchers bury the same two kinds of tea, a slow-rotting rooibos and a fast-rotting green tea, for 90 days at 8 cm deep and weigh what is left. Decomposition starts right after any living thing dies, when microbes break proteins down. Decomposition has two steps. Small animals without backbones first break dead plant and animal matter into smaller fragments, and then soil bacteria and fungi finish breaking it down.
Many soil animals work by comminution, fragmenting leaf litter into pieces. This opens fresh surfaces to microbial decomposers, and some soil animals also graze the microbial community. Heavy farm machines can slow decay. They squeeze soil and cut the flow of oxygen between soil pores, which changes microbial activity and ultimately slows decomposition. Researchers used large rainfall exclusion facilities over forest floors in five forest biomes. With part of the rain kept out, leaf litter lost less carbon and especially less nitrogen, showing that dry weather slows decomposition. Diverse decomposers may protect forests from drought. A more complex community of soil animals softened the slowdown that came when rain was partly blocked, with full compensation when large-bodied invertebrates were present.
Earthworms are soil helpers that belong to a group of segmented worms, the phylum Annelida. Annelids number more than 9,000 species, in three classes: marine worms, earthworms and leeches. Charles Darwin saw earthworms as soil builders. In his 1881 book on worms and vegetable mould he wrote that it may be doubted whether many other animals have played so important a part in the history of the world as these lowly organized creatures. Earthworms tunnel, bury leaf litter and other dead matter and mix it into the soil, and their casts carry minerals that plant roots could not otherwise reach. Some burrow as deep as 2.4 meters. Compared with the surrounding soil, earthworm casts hold about 50 percent more calcium, nitrogen, phosphate, potassium and bacteria, and the calcium carbonate in them lowers soil acidity. Earthworms eat dead leaves and bits of soil where they live.
Not every earthworm helps a forest. Asian jumping worms eat leaf litter at the surface and leave castings low in nutrients that cannot hold water, so they do not recycle nutrients through the soil the way native worms do. Healthy soil teems with life. A single teaspoon can hold more living things than there are people on Earth, and a USDA scientist says all the soil life in one acre equals about two African elephants in weight.
Fungus-farming ants are very old farmers. The ant expert Ted Schultz of the Smithsonian says they have farmed for about 55 million years, while humans have farmed for only about 10,000 to 12,000 years. Fossils tell little about when ants began farming. Schultz says the only fossil fungus-farming ants are in Dominican amber about 15 million years old. Scientists instead use DNA to build family trees that trace the first farmer back 50 to 55 million years. Farming ants and their fungus do not always need each other. In the simpler fungus-farming ants the fungus can live without ants, but in leafcutters the fungus cannot live without them, a true two-way partnership.
Much about fungus-farming ants is still unknown. Schultz says almost half of the species are known only from one collection of specimens in a museum, so scientists know nothing of their biology and must search the tropics for living nests. The ants have used antibiotics for about 55 million years, which puzzles Schultz. The germs that attack the garden could have become resistant, yet somehow the ants keep making antibiotics that still work. To prove that bacteria feed leafcutter ants, a Wisconsin scientist sealed colonies in airtight chambers and gave them air with a rare form of nitrogen, nitrogen-15, as a tracer. After a week it had reached the fungus, the ants and their larvae. Leaves thrown out by the ants hold 26 times more nitrogen than nearby leaf litter and fertilise the soil around them, and plants are more varied near a leafcutter dump.
Some dung beetles dig tunnels under a pile of dung and lay their eggs in it. Dung beetles do many jobs, not just clearing dung. Reviewers list effects on nutrient cycling, soil mixing, plant growth, seed spreading, other animals that live in dung and the spread of parasites. Their jobs depend on their traits. A 2023 review found 66 traits in six groups, such as body form, feeding and movement, and saw that no single group of traits explains how dung beetles respond to or change their world. Dung beetles may help or hurt the climate. In a lab study, cattle dung with a dung beetle gave off 42.2 percent less methane than dung alone, and dung with fly larvae gave off 77.8 percent less, but nitrous oxide rose 23.4 percent with the beetles.
Pill bugs and sowbugs are not insects. They are crustaceans, so they are more closely related to crabs and shrimp than to beetles. A pill bug, also called a roly-poly, rolls up into a tight little ball when it is bothered. Springtails have six legs like insects, but scientists now place them in a separate group. They were once counted as an order of insects, and today they are usually classed as entognathous hexapods, a sister group of the insects.
A springtail has a fork-like part folded under its body that flicks it into the air when it lets go. Springtails live in soil, leaf litter and compost, and they breathe through their skin, so they need damp places. Finding springtails in soil is usually a good sign, because they are signs of living, healthy soil. Springtails that come indoors in search of moisture are only temporary guests. They do not damage a home or breed in it, and they cannot bite or sting.
Heat is a sign of work in a pile. Black soldier fly larvae give off heat as they eat and speed up decay. A working compost pile gets warm too, and the heat comes from the tiny living things that are eating inside it. In a compost pile, tiny living things and small bugs eat old leaves and food scraps and turn them into dark brown compost. In manure, black soldier fly larvae can cut fecal bacteria and other contaminants, and the process can dry the manure, which may make it easier to store and handle.
Words to know
- trophallaxis: food sharing
- eusocial: fully social
- comminution: breaking into pieces
- symbionts: partner microbes
- litterbags: leaf mesh bags
