Do you know which of Darwin’s books sold best when first published?
Heads up, it wasn’t the Theory of Evolution – it was actually his book on worms.
Darwin was both fascinated and impressed by the creatures, stating:
“It may be doubted whether there are many other animals which have played so important a part in the history of the world, as have these lowly organized creatures.”
Although not the first to realize the importance of worms (Cleopatra banned the removal of worms from Egypt under the pain of death!), it was impossible at the time to realize all the benefits worms can bring us.
Now research is uncovering new ways in which we can use worms to benefit the environment – and sometimes help it recover from the damage humans have caused.
How worm mucus combats heavy metals
I was reminded of Darwin this morning when an alert popped up about a new study on worm mucus.
A group of Chinese researchers wanted to find out what would happen when they composted waste containing heavy metals with worms and straw charcoal.
They found that adding mucus could reduce the amount of some heavy metals in compost by up to 11%.
Even larger quantities were changed into a non-accessible form – i.e. a form that can’t harm the environment.
The process accelerated further when the researchers combined worm mucus with straw charcoal (with the exception of one heavy metal).
The study is one of many which show the ability of worms to remove or transform heavy metals.
For example, an Indian study found that up to three-quarters of heavy metals ( cadmium, copper, lead, manganese and zinc) can be removed from waste with worms.
This ensures compost material is well below safety limits and that crops grown are safe for human consumption.
That research found that three species could be used for heavy metal removal: Eudrilus eugeniae (the African Nightcrawler), Eisenia fetida (the Red Wiggler) and Perionyx excavates (the Indian Blue Earthworm).
Meanwhile, South African researchers found that earthworms were able to reduce arsenic and mercury levels in contaminated soils in just two weeks.
What’s more, they also found that the finished compost could clean contaminated water of other heavy metals.
How do they do it?
The worms do this by removing heavy metals from aggregates in the compost in their gut.
San Franciso researcher Chen expanded on this, stating that metals activate an enzyme in a worm’s guts that detoxifies metals in the gut.
However, the Indian study did suggest that dead worms should be removed from the compost.
That’s because at least some heavy metals accumulate in their guts.
However, I’ve seen no mention of the need to remove dead worms from compost material in other studies.
Some worms are getting better at dealing with metals
It’s often humans’ fault that there are high levels of metals in the ground.
But worms may be evolving to deal with metals better.
Nowhere is this more apparent than around mines.
Here worms have quickly evolved in order to live in a very heavy metal environment.
Scientists hope to breed the evolved worms and use them to treat areas contaminated with heavy metals.
What does it mean for composters and vermicomposters?
This is great news for composters, as it shows that worms can improve the quality of compost.
For regular composters, there’s usually no need to add worms to compost, as they find their own way into the compost.
If you’re a worm composter, you may be interested to know that the Indian study found that the African Nightcrawler was the most effective worm for removing heavy metals.
However, the popular red wriggler was also able to remove metals and was found to be effective in more than one study.
How Worms Help Your Compost…
Earth Worms Can Eliminate Antibiotic Resistant Genes
Worms Produce Better Compost Say Researchers
Bait, Worms and Heavy Metals, Why Files
HUAN H H et al, (2023) Effects of earthworm mucus and straw charcoal on heavy metals during domestic sludge co-composting, Chinese Journal of Eco-Agriculture
Pattnaik & Reddy (2011) Heavy metals remediation from urban wastes using three species of earthworm (Eudrilus eugeniae, Eisenia fetida and Perionyx excavatus) Journal of Environmental Chemistry and Ecotoxicology
Singh & Bhartiya (2020) Heavy metal accumulation by earthworm Eisenia fetida from animal waste, soil and wheat (Triticum aestivum) for protection of human health. Research J. Pharm. and Tech