Insects, Breath, and the Carbon Budget
Living organisms move enormous amounts of CO₂ through the air. Insects and other small arthropods dominate animal numbers. That throughput is easy to underestimate — and easy to misread. The climate-relevant fossil pulse is a different quantity: net addition, not recycled breath.
1. An old OZ-ZONE concern, restated
On the site’s long-standing Biology pages runs a persistent theme: the living world is not a footnote. Cell respiration and fermentation are continuous. Small organisms are numerous beyond everyday intuition. Total biological throughput of carbon is easy to under-count if one thinks mainly of mammals — or only of industrial stacks.
That concern was never trivial. Modern counts make it sharper. A 2023 global synthesis puts soil arthropods at about 1019 individuals (roughly twofold uncertainty), mostly mites and springtails, with terrestrial arthropod dry biomass on the order of ~300 million tonnes — comparable in mass to humanity and livestock combined. Plants still hold the great store of living carbon. Head-count and carbon mass are different stories.
2. A back-of-envelope that asks the right shock
Scale a laboratory insect respiration rate (for example a few microlitres of CO₂ per hour) across 1019–1020 individuals and a season, and the gross volume of CO₂ becomes enormous — in the same conversation as, or larger than, annual fossil emissions, depending on the assumptions. The shock is useful. It forces attention onto living throughput.
The same envelope is not a global inventory. Most of those individuals are not fruit flies. Metabolic rate depends on size, temperature, and activity. Global carbon accounting is built from ecosystem and soil fluxes, not from one culture multiplied by a planetary head-count. The envelope is a scale argument, not a substitute for a measured insect-only line in the budget.
3. Insects produce CO₂ — they do not absorb it as plants do
Insects do not photosynthesise. They take in organic carbon with food and release CO₂ through respiration. Relative to atmospheric CO₂ uptake, an insect is a source, not a sink. The carbon in that CO₂ was almost always fixed earlier by plants (or by organisms that ate plants). Death and microbial decay return remaining body carbon to the cycle as well.
4. Why that CO₂ is recycled carbon
The fast loop is simple:
air CO₂ → plant tissue → insect food → insect CO₂ → air again (and onward into the next round of growth).
The carbon atoms are moving through a shared surface pool. Insect breath is throughput. It is not, in the main, carbon mined from geological stores. Fossil coal, oil, and gas are different: carbon locked away for millions of years, returned to the air by combustion and industry as a net addition to the active pool.
5. How much CO₂ do insects produce?
There is no single, tight public line item labelled “all insects, all CO₂, one year” comparable to fossil-fuel inventories. What is measured more robustly:
- Terrestrial ecosystem respiration (plants + microbes + animals) is on the order of ~100 Pg C per year.
- Heterotrophic respiration (consumers and decomposers) is on the order of ~40–50 Pg C per year, dominated by soil microbes, not by insects alone.
- Fossil carbon addition is on the order of ~10 Pg C per year in recent years (about 35–37 Gt CO₂ as fossil CO₂ mass).
Insects sit inside the heterotrophic slice. Their gross CO₂ is real and continuous; it is not the bulk of the measured land respiratory flux. Human and livestock breath together are about 1–1.5 Pg C per year — also recycled food carbon, and still small next to soils and plants.
6. Can a stronger plant–insect circle cancel the fossil extra?
The hopeful sequence is familiar: more CO₂ → more plant growth → more fauna → more carbon held in living systems → compensation “in time.”
Parts of that sequence are real. CO₂ fertilisation can favour growth where water and nutrients allow. Land and ocean sinks already take up a large share of each year’s anthropogenic CO₂. Some regions have greened. The biosphere and oceans do respond.
They do not respond completely on the schedule of the industrial pulse. A large residual remains in the air every year. That is why the measured concentration rose from about 280 ppm toward 420+ ppm. If the plant–insect loop fully cancelled fossil carbon on human timescales, that sustained rise would not be observed.
Further limits: growth is constrained by water, nitrogen, phosphorus, land, heat, and disturbance; clearing can release carbon; much uptake is oceanic, with acidification as a companion; insects amplify throughput more than they build the long-term vault. The vaults that matter for storage are lasting biomass, soils, and the ocean — and even those have not matched fossil input one-for-one.
7. What a competent reading keeps together
| Claim | Status |
|---|---|
| Small arthropods dominate animal numbers; living throughput is easy to underestimate | Supported — and central to the Biology pages’ long concern |
| Gross insect CO₂ can look huge next to industry in a scale argument | Plausible as illustration; not a precise global insect inventory |
| Insect CO₂ is mostly recycled plant carbon | Established process |
| Fossil CO₂ is a net addition from geological stores | Established process |
| Biosphere + ocean fully cancel the fossil pulse in time | Not supported by the atmospheric record or carbon budgets |
8. Closing
OZ-ZONE’s biological instinct was never the claim that insects “do not matter.” It was the claim that models and public talk under-weight living numbers and living flux. That instinct stands on firmer ground when it is joined to the other half of the method: gross recycled throughput is not the same quantity as net fossil addition, and the Earth system’s response to the latter is strong, partial, and already visible in the air.
Hold both. The small animals really are legion. The fossil pulse really does accumulate. Clarity begins when those sentences are no longer forced to cancel each other.
Sources (minimum set)
- Rosenberg, Y. et al. (2023). The global biomass and number of terrestrial arthropods. Science Advances 9, eabq4049.
- Bar-On, Y.M., Phillips, R. & Milo, R. (2018). The biomass distribution on Earth. PNAS 115, 6506–6511.
- Global Carbon Budget updates (Friedlingstein et al., ESSD) for fossil and sink orders of magnitude.
- Observation-based terrestrial respiration syntheses (ecosystem and heterotrophic fluxes, Pg C yr−1).
- OZ-ZONE Biology — long-form site context on living systems and measurement.
Figures are explanatory schematics for orientation, not reproductions of a single published plot. Pg C = billion tonnes of carbon. Multiply by ~3.67 for approximate CO₂ mass equivalent where that conversion is appropriate.