While there are hundreds of species of earthworms, anyone who makes compost knows the redworm, or Eisenia fetida. They make what's considered perhaps the richest form of natural fertilizer — a true friend to farmers and gardeners alike.
What you might not know is that very low levels of pesticides can kill these "black gold" producers. If they don't kill outright, pesticides can cause other serious harm, like reducing worms' ability to reproduce. Exposure to the neonicitinoid pesticide imidacloprid — well-known for its toxicity to honeybees — can also cause serious harm to worms, damaging DNA and deforming sperm. Bad news.
A recent study in the journal Chemosphere showed that endosulfan and the carbamate insecticides aldicarb and carbaryl were all lethal to redworms at levels up to 10 times lower than the recommended agricultural doses (0.025, 35 and 20 mg/kg soil respectively). Three other pesticides (cypermethrin, chlorpyrifos and monocrotophos) were lethal as well but at levels roughly 5 - 10 times higher than the recommended dose.
An earlier report in Environmental Toxicology and Chemistry showed that 2 other carbamate insecticides were classified as extremely toxic to worms. Most surprising, however, was the finding that the breakdown products of 4 pesticides (parathion, carbaryl, 2,4-D and 2,4,5-T) were just as toxic — or even more so — than the parent material.
Damaging even when not deadly
Whether you’re mammal, amphibian, bird or annelid (worms), immediate death is not the only important outcome from exposure to hazardous pesticides. Other health outcomes include birth defects, cancer, developmental or reproductive harm, to mention the big ones.
Among worms, non-lethal impacts include affecting the ability to produce cacoons or sperm, reducing the numbers of those beautiful, tiny yellow/brown translucent pearls you see scattered through your compost.
So while choosing to grow or buy organic not only protects the health of children, it makes worms (and soil!) happy and healthy too.