Do Weeds Matter for Biodiversity?

October 14, 2020

Weeds. A very negative-sounding word for many. However, weeds might not exactly be what we used to think they are. Let me take you on a walk in the countryside, observing fields of barley as we pass them by. In the meanwhile, let’s explore who weeds really are. Let’s find out: do weeds matter for biodiversity? And how much?

I bet only few of you have ever seen a field as the one on the picture. Even as an attentive observer of the farmlands around me, I haven’t seen such a colourful cereal-field before, until I saw this one at my faculty of agricultural sciences. At this test plot, no herbicides have been applied, allowing the weeds to come to full bloom in summer. Maybe those from the older generation will remember such blooming fields from the time when they were young, but it has become a rare sight nowadays.

Barley field full of blooming weeds

Barley field full of blooming weeds. Photo by Naomi Bosch

While the flowers are exceptionally beautiful to look at, this is not an homage to the good old times, when “everything used to be better”. Neither does this text mean to condemn all the farmers of the world who do apply pesticides. In fact, its purpose is to strike up a debate about flowers, bread, bees and biodiversity. About who is and who isn’t paying the cost for the cornflowers and poppies we don’t see around us anymore.

Unwanted weeds

There is no doubt that the blue and red spots of flowers in the field of cereals on the picture are a pretty sight. But this doesn’t change the fact that those are weeds. Weeds are any plants that grow on the field along with a crop, that haven’t been sown there intentionally.

Those nasty plants may grow very quickly after sowing and overshadow the crop, “stealing” light, water and nutrients from it. When the weeds are left in the field until harvest, they will cause quite a number of problems. First, they get entangled easily in the turning wheels of the harvester, making harvesting slower and more complicated. And the residues of the unwanted plants, like seeds or leaves, will have to be filtered out of the harvested material since otherwise, they can spoil the crop by making it too moist or dirty. In some cases, weeds can even be poisonous for humans or animals, who will eat the crop at the end of the day.

Battling with weeds

Most of human history has been the story of battling with weeds. Even in the earliest chapters of the Jewish Torah, weeds are mentioned as the enemy of man:

“Cursed is the ground because of you; through painful toil you will eat food from it all the days of your life. It will produce thorns and thistles (=weeds) for you, and you will eat the plants of the field.” (1)

Thorns and thistles are weeds that cost farmers a lot of work, sweat and money

Thistles have cost farmers much work, sweat and money. Photo from Unsplash

Agriculture – “agri-culture” – mostly means culturing one single crop on a plot of land, something that is deeply unnatural in wild ecosystems. There’s always a multitude of different species that co-exist in the wild. So, nature will be prompted to intervene in this man-made monotony by letting weeds grow in between. Man, on the other hand, will always try to get rid of these intruding plants.

The web of life

But why bother about weeds? Why not make order on our farmland and wipe them out if we can? Why ask where have all the flowers gone?

In her book Silent Spring, Rachel Carson writes in 1962:

“The earth’s vegetation is part of a web of life in which there are intimate and essential relations between plants and the earth, between plants and other plants, between plants and animals. Sometimes we have no choice but to disturb these relationships, but we should do so thoughtfully, with full awareness that what we do may have consequences remote in time and place. But no such humility marks the booming ‘weed killer’ business of the present day, in which soaring sales and expanding uses mark the production of plant-killing chemicals.”

With razor-sharp truth, Rachel Carson described a reality which we now face.

Which kind of reality?

The price of biodiversity

To understand this, we must go back to the story of agriculture – “agri-culture” – once again. The story of humans growing the food to live on, of intervening in nature to make life possible for themselves. Definitely an understandable endeavour! But at what price?

A field without weeds doesn't support biodiversity as much

A barley monoculture that is in stark contrast to the diverse barley field seen above.
Photo by Naomi Bosch

Diverse ecosystems had to make room for monocultures of single crops, intensively managed with chemical pesticides. With ever more efficient, ever more ingenious techniques, man appropriated the whole natural world to himself, to the point of killing off each and every organism that would come into his way. Or in his profit’s way. It’s what we call our modern industrialized agriculture.

Unfortunately, this kind of industrialized agriculture didn’t come without its negative consequences. Those “consequences remote in time and place” that Rachel Carson had foreseen more than 60 years ago.

Synthetic pesticides emerged in the 20th century. Farmers and officials started to intensively use them after world-war two, proclaiming the long-sought victory over pests of every kind – insects, fungi, weeds. And all was well…

Or not?!

Victory & defeat

Soon, an unintended side-effect emerged. Some insects, fungi and weeds developed a resistance to the chemicals. So-called “super-weeds” and other pests remained untouched by the rain of pesticides (which happens naturally when one “weapon”, in this case weed killers, is used too intensively). When pests become resistant to a chemical, the pesticide becomes useless and we’re in real trouble. Because now we have populations of super-adapted pests and a “weapon” that’s rendered completely useless! And this phenomenon is happening more and more often in agriculture.

And then we have to face a scary question: what if the enemy that we were trying to fight with our chemical weapons wasn’t who we thought he was? Or if he wasn’t an enemy at all?

Do weeds matter for biodiversity?

However bad and annoying weeds are to farmers, they do, as a matter of fact, have an important role in nature and farming! Just now, we are at a turning point. We are rediscovering the significance of weeds, while we are simultaneously unveiling the dire consequences that their eradication has had on our planet…

So why do weeds matter?

Do weeds matter for biodiversity?

Do weeds matter, after all? Photo by Naomi Bosch

Redefining “weeds”

First of all, weeds fill out the blank spaces farmers leave after harvest or while sowing their crop. Uncovered soil is a deeply unnatural thing, so nature’s quick to cover it up so that precious topsoil, nutrients and water don’t get wasted. Weeds prevent soil erosion by creating a pioneering green cover on the bare soil.

Weeds protect soils from erosion

Weeds create a dense cover protecting the soil from erosion. Photo by Naomi Bosch

Also, people eat (or used to eat) many weedy plants on a regular basis! Some of our vegetables wouldn’t even exist if it weren’t for weeds. Just one example is arugula, a popular, tasty and healthy type of salad that used to be considered a weed!

And just as all plants, weeds are a home and a source of food to a number of animals. Weeds matter for the biodiversity of all kinds of creatures.

Think, for example, of insects visiting flowering weeds or of birds eating their seeds.

Homeless insects… or why weeds matter for biodiversity

The 50 most common weed species in Germany are food and home to a staggering 5000 insect and bird species! And there are many more species dependent on weeds than we know of, as possibly just a tenth of all insect species worldwide has been described up to date. In reality, weeds matter far more for biodiversity than we have long believed!

So, weeds do not only harm crop production. They do offer an array of amazing benefits to all of us, including farmers. For example, researchers found out that the bright blue cornflowers – which are weeds, too – specifically attract hoverflies. Hoverflies are true friends, as they pollinate plants and eat aphids, a feared crop pest. When hoverflies and other so-called natural enemies of pests (such as ladybugs) are attracted to the field by weeds, they devour aphids!*

Weeds attract beneficial insects

Cornflowers attract beneficial insects, such as hoverflies. Photo by Naomi Bosch

A field without any weeds, as has become the norm, won’t attract as many of these friends. If, in addition, aphids are killed with an insecticide, the hoverflies and ladybugs get killed in the same movement. This strips nature of its ingenious mechanism called biological pest control.

What we are losing when we lose biodiversity

The trouble is, we don’t really know what we’re losing when we’re losing the weeds. So many of nature’s incredible ways still remain a mystery to us. But what we are coming to certainly understand is that we have a serious problem with the global biodiversity loss.

Biodiversity, that’s the diversity of all things alive: plants, animals, bacteria, fungi, humans… basically all the different forms and species of living organism.

The sixth mass extinction

The World Wide Fund for Nature International (WWF) found that between 1970 and 2016, we lost 60% of wildlife globally.

Pollinators, such as bees and hoverflies, are in decline all over the world. Over one third of all food crops depend on insect pollination. And thousands of other pollinators help increase crop yield.

Pollinators depend on weeds to thrive

Pollinators are indispensable for our survival on Earth. Photo by Naomi Bosch

A collapse of farmland bird populations has been observed for decades. As much as 100 years ago, people already started noticing that there were fewer birds around!

And a recent study undertaken in protected (!) areas in Germany found that a staggering 75-80% of insects have been lost in just 27 years.

If you hope that things look better outside of Germany, I have to disappoint you. From all ends of the planet, word is coming in about the worrying decline of biodiversity.

From Costa Rica to Romania, from the UK to South Africa, biodiversity, and specifically that of insects & birds, is plummeting.

Should this surprise us? Unfortunately, no. And we have known it for quite some time already.

Does it surprise us that insects and birds are disappearing when such diverse fields full of life are gone? Video by Naomi Bosch

Dire truths

Simply speaking, insects (just as all other creatures) need a place to live in and find food. They find both of these mainly in plants. And you’ve guessed it, this includes what we call weeds. So, do weeds matter for biodiversity? Definitely!

Herbicides and a reduced crop-rotation (among others) have wiped out weeds. And this to the point of reducing the biodiversity of weeds by 70%! Many weed species that used to be very common in the past are now virtually extinct.

So, if we destroy the basis of existence for insects, birds etc., it’s logical that they will disappear along with the weeds they depend upon. Even more so knowing that some insects and birds specifically depend on a single plant/weed species to live! If this weed species becomes extinct, the creature linked to it inevitably becomes extinct, too.

If weeds disappear, the associated diversity of life will vanish because weeds are incredibly important for biodiversity.

It’s time to ask, quite literally, just as in that famous song:

Where have all the flowers gone?

Biodiversity sustains us all

In nature, everything is connected. Without biodiversity, without this tight and diverse web of life sustaining us all, we’re as good as dead. It’s a slow death we certainly want to escape.

A study from 2020 notes that habitat destruction and agricultural intensification (including pesticide use) are some of the major drivers of insect loss. (2)

However, before we put all the blame on farmers, we should consider carefully what habitat destruction really means, and who drives agricultural intensification. A potential habitat for plants, insects, birds etc., that’s technically everywhere on the planet. Including the places where we live, study, go shopping, build streets and parking lots… And agricultural intensification, that’s the cheap bread we had for breakfast or the biofuel that gets us to work in the morning.

Can the way we grow cereals for bread support biodiversity?

Can bread give life? Photo by Naomi Bosch

Pointing fingers and blaming won’t get us anywhere. So, let’s focus on solutions instead! Just as we all are, in one or the other way, part of the problem, we can all become part of the solution!

From problem to solution

This global biodiversity crisis starts with the pretty cornflowers shaking in the wind on a splendid summer’s day. It continues in the sweat and wallet of the farmer reaping the year’s harvest in an effort to put food on the table for his children. A bloody spectacle in the sky, the sun sets over the dusty field, just to rise again on a crisp autumn morning. It’s Sunday morning, and in churches all over the world people are giving thanks for God’s creation and the people putting the food on our tables. Breaking the freshly baked bread, so reminiscent of sweet childhood memories, we remember what makes life possible for all of us.

Bread. Christ.

Can our breaking of bread, our savouring of this life-giving substance, give life itself?

What we eat, how we eat, determines whether or not life will be possible on our planet in the future. And not just any life!

The good life we all long for.

How do you think we could start a change? How do our food choices impact biodiversity &the environment? Did you know that weeds matter for biodiversity?

More on biodiversity & weeds

This article is mainly based on my Bachelor thesis. Click the button below to read the full text of my thesis, including all the references I’ve used:


Read more about this topic in my other articles about biodiversity & farming:

* Unfortunately, matters are just not as simple as that. While hoverflies and ladybugs do a brilliant job at fighting aphids, especially in a smaller garden setting, they can’t devour them all at once… And a major problem with aphids is that they transmit plant viruses that can’t be fought any other way than by wiping out the transmitting aphids. Does the price of chemical insect control justify the ecological consequences? And how would an ecologically intact and resilient agroecosystem react to an attack of aphids/viruses? Questions to which I don’t have a full answer yet. Let me know if you have any thoughts on that!

(1) The Bible: Genesis 3, 17-18

(2) Wagner, David L. (2020): Insect Declines in the Anthropocene. In Annual review of entomology 65, pp. 457–480. DOI: 10.1146/annurev-ento-011019-025151 .


Teaser photo credit: Photo from Unsplash.

Naomi Bosch

grew up in Croatia, having a garden & nature close by. In 2017, I moved to the North of Germany to study agriculture. I have worked on various farms since. To me, it is always a pleasure to work in agriculture and discover the way farmers live. Through this blog, I want to invite you on a journey to discover plentiful lands all around us.

Tags: agricultural biodiversity, Building resilient food and farming systems, weeds