How Do Earthworms Change Soil Structure?
As an Amazon Associate we earn from qualifying purchases.
How do earthworms change soil structure? The sources name three routes: casts, gut mucus and burrowing. Soil structure is the arrangement of particles into aggregates and the pore networks between them, and the review ties earthworms to both. One bibliometric review of earthworm research says the literature “mainly reports the ecological effect of earthworms on soil structure, nutrient cycling, soil biota, soil ecosystem services and greenhouse gas emissions.” This article explains the mechanisms named in two peer-reviewed sources and notes where the evidence stops.
Quick answer
- Earthworm casts help bind soil. The review reports that “Earthworm cast increases the aggregate stability and proportion of macroaggregates.”
- Gut mucus helps form larger aggregates. The same review says “The mucus secretion by earthworms’ guts is also beneficial for the formation of macroaggregates.”
- Burrowing changes pore space. The review describes earthworms enhancing “soil porosity” through “swallowing, excreting and burrowing.”
- The wider soil biota matters too. A meta-analysis finds “a clear positive effect of soil biota on soil aggregation.”
What soil structure means
Soil structure is not the same as soil texture. The meta-analysis defines it clearly: “An essential feature of soil that allows it to provide these important functions is its structure: the arrangement of soil particles into aggregates and associated pore networks.” Texture describes the mix of sand, silt and clay, while structure describes how those particles are grouped and how the spaces between them connect.
The meta-analysis also explains why structure matters for the rest of the soil system. It says that soil structure “provides the stage for soil’s immense biodiversity” and “exerts key controls over all soil-borne biogeochemical processes.” A change in structure therefore affects the living community, water movement and nutrient cycling together.
Casts and the cementing of aggregates
Earthworm casts are one of the clearest links between worms and structure. The review states that “Earthworm cast increases the aggregate stability and proportion of macroaggregates, likely due to the cementation of soil aggregates by high Ca in the soil.” The mechanism named here is cementation by calcium.
The review presents cast cementation as a stated mechanism and attributes the calcium link to earlier studies. The fetched text therefore reports the link rather than measuring it.
Mucus and the formation of macroaggregates
Gut secretions are the second mechanism. The review says that “The mucus secretion by earthworms’ guts is also beneficial for the formation of macroaggregates.”
For the main question here, the key point is that mucus is named as a factor that supports larger aggregates, not that it creates every aggregate in a soil.
Burrowing and pore space
Burrowing is the third mechanism, and it changes how air and water move. The review reports that earthworms improved soil conditions “to promote plant biomass by swallowing, excreting and burrowing,” and it names the change as “enhanced soil porosity.”
Burrows also change the life that lives in the soil. The review states that “the burrows of earthworms are beneficial for increasing the abundance, diversity and activity of the soil microbial community.” The review says the burrows also speed decomposition: they accelerate “the decomposition of soil organic matter” compared with control soil without earthworms.
How the research frames the effect
Research on earthworms moved over time. The review notes that “In the earliest stage, researchers focused on the role of earthworms in shaping soil structure and fertility.” Later work widened the focus, and the review reports “more than 200 papers published every year” in the later period, with many papers focusing on “the effects of earthworm invasion on soil structure, native soil food webs and nutrient availability.”
The effects also depend on the worm. The review reports that “the effects of earthworms on soil properties depended on the total biomass and the feeding and burrowing habitats of earthworms.” That finding is important for gardeners because it means the same species may not act the same way in every soil, and it may behave differently in beds with different amounts of organic matter.
The review also reports a pattern tied to invasion. It states that exotic earthworms “played an important role in regulating soil structure and function in northern temperate forest ecosystems in the last few decades.” That is a regional finding, so it should not be read as a rule for every garden bed.
Where earthworms sit among soil organisms
The meta-analysis ranks groups of soil organisms. It says that “bacteria and fungi generally appearing more important for soil aggregation than soil animals.” It also notes that “Bacteria contribute strongly to both macro- and microaggregates while fungi strongly affect macro-aggregation.” Earthworms are soil animals, so the meta-analysis suggests they are not the largest factor in aggregation.
The same meta-analysis places earthworms inside a wider picture. It concludes that “At the broadest level our results highlight the need to consider biodiversity as a causal factor in soil aggregation.” For a bed or lawn, that means earthworms are one part of a community, and fungal threads and bacterial products are also part of the structure.
For a closer look at the gut process that feeds this structure, see how earthworms digest soil in their gut. For the binding mechanism in more detail, see how earthworms hold soil particles together with mucus.
How we chose
Two open-access articles from PubMed Central were selected. One is a bibliometric review of earthworm research, and the other is a meta-analysis of soil biota and aggregation. Both URLs returned HTTP 200 when checked on 2026-10-28. Quotes come from the fetched pages. The selection favored sources that discuss the mechanism of structure change rather than general garden advice.
What we could not verify
The sources do not give a single rate at which earthworms change structure in a garden bed. They name mechanisms and effects, but they do not convert them into a time schedule, a worm density, or a quantity of casts for a particular soil.
What the sources do not say
The meta-analysis does not single out earthworms. Its key groups are bacteria, fungi and animals, and the quoted statement compares fungi and bacteria with “soil animals” as a group. The fetched text therefore does not give a separate earthworm ranking.
The review is a bibliometric study of publications, so many of its statements summarize other research rather than report new measurements. For example, the statement about cementation by calcium is attributed within the review to earlier work. The fetched text does not supply the original trial data, so the calcium mechanism should be treated as reported rather than measured here.
Frequently asked questions
Do earthworms make soil looser?
The review says earthworms “enhanced soil porosity” through “swallowing, excreting and burrowing.” The fetched text does not give a density or texture measure that quantifies the change in every case.
What is an earthworm cast, and does it help soil?
A cast is the material an earthworm passes out. The review states that “Earthworm cast increases the aggregate stability and proportion of macroaggregates.” The stated cause is cementation of aggregates by calcium in the soil.
Does mucus from earthworm guts matter for soil?
The review says mucus is “beneficial for the formation of macroaggregates.” It is named as a binding factor, and the same review places it alongside casts and burrows as part of the structure effect.
Are earthworms more important than fungi or bacteria for soil structure?
The meta-analysis says the opposite is generally true for aggregation. It states that bacteria and fungi “generally appearing more important for soil aggregation than soil animals.” Earthworms are included in the animal group, so they are not presented as the leading factor.
Can earthworms harm soil structure?
The sources do not describe a harmful effect in the fetched text. The review does say that the effects “depended on the total biomass and the feeding and burrowing habitats of earthworms,” which means outcomes vary with worm type and soil conditions rather than always being positive.
Sources
- Lehmann, A., et al. “Soil biota contributions to soil aggregation.” doi:10.1038/s41559-017-0344-y. https://pmc.ncbi.nlm.nih.gov/articles/PMC5701735/ (HTTP 200, checked 2026-10-28)
- “A Bibliometric Analysis on Research Progress of Earthworms in Soil Ecosystems.” https://pmc.ncbi.nlm.nih.gov/articles/PMC11201220/ (HTTP 200, checked 2026-10-28)
