Glyphosate kills bees by stealth

November 2018

Increasing suspicion is falling on glyphosate herbicides' effects on microbes in the gut of consumers.

The innards of all animals are teeming with bacteria whose quantity and diversity exert multiple influences on health.  Many of these microbes have enzymes in common with plants, and, like plants, can be harmed when glyphosate interferes with them.

Our major pollinators, honey bees and bumble bees, can easily be exposed to glyphosate when foraging on weeds which have been sprayed or wild-flowers which have been caught in spray drift, or on GM herbicide-tolerant crops which accumulate the glyphosate applied to them.

When American scientists fed environmentally-relevant doses of glyphosate to honey bees, they noted a reduction in the presence of all eight bacterial species normally dominant in the bee gut.  Such microbes play a vital part in the healthy development, nutrition and immune system of bees.  Perturbation of the gut community won't kill the bee, but will make it vulnerable to environmental stressors which can be lethal.  Moreover, since newly-emerged worker bees effectively inherit their gut microbes through social interaction with older workers, they may acquire a sub-optimal gut flora during the earliest part of their lives when their health can be most easily damaged, and even before they visit any contaminated flowers.

Further experiments investigating the implications for the bees' immune system when their gut microbe balance is disturbed found that glyphosate-treated bees became susceptible to opportunistic pathogens.  The loss of one dominant glyphosate-sensitive bacterium in particular is thought to have major implications for immunity.  This microbe produces anti-microbial substances which could protect against infection, and, because it forms a lining on the gut wall, could act as a physical barrier to pathogen invasion.  It's also thought to play a critical role in enabling the healthy gut flora to assemble.

Interestingly, in parallel to a study of rats fed glyphosate [1], the bees' gut flora seemed to be more affected by the lower dose of the herbicide.  Like the previous study, this hasn't been explained, but in the present case it's possible the worst-affected bees never made it back to the hive to be tested, either because they were dead or because they were too befuddled [2,3].

The very real possibility of nutritional impairment due to poor feeding [3] or poor digestion when glyphosate was present in the bees' food wasn't addressed.

More than a decade ago, US beekeepers began finding their hives decimated by what became known as 'colony collapse disorder'.  Millions of bees mysteriously disappeared leaving farms with fewer pollinators for crops.  Explanations for the phenomenon have included exposure to pesticides or antibiotics, habitat loss, and infections.  Regulatory guidelines assume a weed-killer won't harm bees.  This latest study suggests otherwise.

The bigger picture is that 40% of pollinator species including butterflies and bees are facing extinction, and glyphosate might be another nail in their coffin.


Glyphosate is known to arrest bacterial growth without killing them.  None of the adverse gut effects described above are directly toxic, but could contribute significantly to a fatal outcome in all sorts of indirect ways.

This study casts an interesting new light on the vanishing Monarch butterflies in America [4]: habitat and food-loss certainly play a part, but indirect effects of glyphosate on their gut flora too could make a significant contribution to disaster.

There's no reason to think that humans will fare any better on a glyphosate-laden diet than do the butterflies and bees.

[2] BEES WITH DEMENTIA - September 2015
[3] BEFUDDLED BEES - June 2018

·         Glyphosate linked to bee deaths, GM Watch 25.09.18
·         Erick V. S. Motta, et al., 2018, Glyphosate perturbs the gut microbiota of honey bees, PNAS
·         Kathy, Good Energy On: Climate - The Butterfly Thief, Living Earth, Winter 2017

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