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Earthworms are vital to sustainable soil fertility. Up to 1000 individuals in each square meter of land act as ecosystem engineers: they shred plant litter and process it in their gut making nutrients available to plants; their burrowing aerates the soil and enhances water- and root-penetration.
Chemicals which harm the worms in soil are bad news.
Although it's heavily used on GM crops because most have been transformed to tolerate it, the very idea that glyphosate herbicide (active ingredient of 'Roundup') could be detrimental to earthworms has barely been entertained. After all, this chemical interferes with a biochemical pathway found only in plants, and the plant litter generated by the dying weeds will provide extra food for the worms. Glyphosate is obviously safe for animals, and obviously has benefits for nature.
Or does it?
Science says otherwise.
Austrian scientists set up experimental near-realistic weedy ecosystems. They added two agriculturally common species of earthworm with different life-styles (one a vertical burrower, the other a horizontal burrower). Then they dosed half with an agriculturally low concentration of glyphosate for four consecutive days and measured what happened.
The weeds in herbicide-treated plots died within a couple of days. This had significant effects on the soil. With the super-fast artificially-induced plant death and no living plants to take up nitrate and phosphate, the levels of these minerals shot up, with the likely consequence that, in a 'real' ecosystem, they would then leach out of the soil. Soil moisture, known to bolster earthworm activity, increased dramatically in the absence of plants to draw it up and release it to the atmosphere. Also, there were signs that the decomposition of some soil constituents had slowed due to their conversion to a more stable form.
Using the number of worm casts (manure) on the surface of the soil as an index of burrowing and feeding activity, the authors found that vertical burrowers demonstrated the expected increased activity in response to the herbicide-generated presence of litter and moisture: this was followed, however, by a catastrophic decline in both number and size of the casts. The activity of the horizontal burrowers further below the surface was unaffected. Extended experiments are needed to investigate whether glyphosate-avoidance behaviours might be affecting the surface activity of both types of worm.
Measures of reproductive success after exposure to the herbicide demonstrated severe harm to both worm species. The numbers of cocoons were more than halved by glyphosate, and this failure was compounded by a similar reduction in the numbers of young hatching from the few cocoons present.
Although the replication of treatments in the experiment was insufficient to permit statistics, there are all the signs of an earthworm colony collapse every bit as bad as what's happening to our bees.
The authors comment:
"Obviously, official testing of potential side-effects during registration procedures failed to identify these ecologically important impacts. Although productivity in many agricultural systems depends on the use of pesticides, findings from our study strongly indicate that more serious attention has to be paid to testing pesticides for potential undesirable ecological side effects, especially in light of the projected doubling of global pesticide use by 2050."
It looks like glyphosate actively inhibits the very formation of healthy soil: it has antibiotic properties which kill the microbes necessary for nutrient release, it makes the soil less degradable, it reduces earthworm activity and all but wipes out their future generations.
Glyphosate has been on the market for decades without any more meaningful safety testing of its effects on the soil than of its effects on humans. The 'projected doubling of global pesticide use' over the next generation sounds like a recipe for human colonies to follow in the footsteps of the bees and earthworms.
Support a ban on glyphosate before any more harm's done.
 ROUNDUP ANNIHILATES EARTHWORMS - January 2015
- Mailin Gaupp-Berhausen, et al., 2015, glyphosate-based herbicides reduce the activity and reproduction of earthworms and lead to increased soil nutrient concentrations, Nature Scientific Reports, 5.08.15