Why Do Coffee Plants Make Caffeine? Pesticides, Bees and Evolution

Why do plants make caffeine? Not for us. For a coffee plant, caffeine is a chemical tool: it is bitter and toxic to many insects, it may hold back competing plants around the tree, and in small doses in nectar it helps pollinating bees remember coffee flowers. The fact that it also keeps humans alert is a happy accident of chemistry.

What makes the story even better is that coffee is not the only plant that discovered this trick. Tea, cacao and citrus make caffeine too, and the coffee genome shows that coffee plants invented their own way of making it. Here is what researchers have found.

Key takeaways

• Caffeine works as a natural pesticide: a 1984 study in Science found it disrupted feeding, growth and reproduction in a range of insects.
• Coffee seeds release caffeine that can inhibit other seeds, a form of chemical competition called allelopathy.
• In 2013, researchers showed that caffeine in coffee and citrus nectar helps honeybees remember a flower’s scent, making them more loyal pollinators.
• The 2014 coffee genome revealed that coffee evolved its caffeine-making genes independently from tea and cacao: a case of convergent evolution.
• Robusta beans contain about twice as much caffeine as Arabica.

In this article

1. Caffeine as a natural pesticide
2. Chemical warfare in the soil
3. Caffeine and bees
4. One molecule, invented several times
5. Why Robusta has more caffeine
6. The pest that beat caffeine
7. FAQ

Caffeine as a natural pesticide

Plants cannot run from the animals that eat them, so many defend themselves chemically. Caffeine belongs to a family of nitrogen-containing compounds, the alkaloids, that includes many plant defenses.

In 1984, Harvard neurobiologist James Nathanson published a paper in Science titled “Caffeine and related methylxanthines: possible naturally occurring pesticides.” Testing insects such as tobacco hornworm larvae, mealworms and mosquito larvae, he found that caffeine and related compounds could disrupt their behavior, reduce feeding and inhibit reproduction, often fatally at higher doses. Part of the explanation is that caffeine interferes with enzymes in insects’ nervous systems.

For the coffee plant, that means leaves and seeds laced with caffeine are less attractive to many plant-eating insects. The caffeine is concentrated in the parts the plant most needs to protect, including young leaves and the seeds, which are the beans we roast.

Chemical warfare in the soil

Caffeine may also help coffee plants compete with other plants. In a 1983 paper in the Journal of Chemical Ecology, Jacob Friedman and George Waller studied coffee seeds as “allelopathic agents.” Allelopathy means a plant releasing chemicals that suppress the growth or germination of other plants.

They identified caffeine as an inhibitor released by Coffea arabica seeds and found that the release increased sharply as seeds aged and broke down. The idea is that caffeine leaching from fallen seeds and fruit into the soil could slow down rival plants trying to grow nearby.

There is a twist: the same researchers also studied the hazards of caffeine to germinating coffee seeds themselves. Caffeine is a powerful chemical, and too much of it in the soil may not be good for young coffee plants either. Like most defenses, it is a balance.

Caffeine and bees: a memory booster in the nectar

If caffeine repels insects, why would coffee flowers put it in their nectar, the sugary reward meant to attract pollinators? A team led by Geraldine Wright at Newcastle University answered that in a 2013 paper in Science, “Caffeine in floral nectar enhances a pollinator’s memory of reward.”

• They found caffeine in the nectar of both Robusta and Arabica coffee flowers, and in citrus flowers such as grapefruit, lemon, pomelo and orange.
• The amounts were low, too low for bees to taste as bitter. High concentrations, by contrast, repel honeybees.
• Bees trained with caffeinated sugar solution were three times more likely to remember a flower’s scent 24 hours later than bees given plain sugar, and twice as likely after three days.

The benefit for the plant is clear: a bee that remembers coffee flowers is more likely to return to them and carry coffee pollen to other coffee plants, which improves pollination. Caffeine, in other words, turns casual visitors into loyal customers.

One molecule, invented several times

Coffee, tea and cacao all make caffeine, and they are not close relatives. Did they inherit the ability from a shared ancestor, or did each one evolve it separately?

In 2014, an international team led by France Denoeud and Philippe Lashermes published the genome of Coffea canephora, the Robusta species, in Science. They found that coffee’s genes for making caffeine, enzymes called N-methyltransferases, had expanded through a series of gene duplications. Crucially, those genes evolved independently of the comparable genes in tea and cacao.

That is convergent evolution: unrelated species arriving at the same solution because it works. Wings in birds and bats are a classic example. Caffeine is a chemical one. When several plant lineages build the same molecule from different genetic starting points, it strongly suggests that caffeine gives a real survival advantage.

Why Robusta has more caffeine

Robusta and Arabica are different species. A 2023 study of green beans from Lombok’s Geopark Rinjani in Indonesia measured an average of about 1.09% caffeine in Arabica and 2.09% in Robusta, close to double. Other studies on Arabica alone report values in a similar range, around 0.9 to 1.3% of the bean’s dry weight.

Why the difference? Researchers have not settled on a single answer. Robusta is a different species with its own set of caffeine genes, and the genome study showed those genes had multiplied in C. canephora. Robusta also typically grows at lower, warmer altitudes than Arabica, where insect pressure is generally higher, and a stronger chemical defense would make sense there. That ecological explanation is plausible, but it is a hypothesis rather than a proven cause.

For coffee drinkers, the practical result is simple: Robusta tastes stronger and more bitter, makes thick crema, and delivers more caffeine per gram. We compare the two species in more depth in our guide to the best coffee beans in the world.

The pest that beat caffeine

Every defense invites a counterattack. The coffee berry borer, a tiny beetle, is the most damaging insect pest of coffee worldwide, and it lives inside the very seeds that are richest in caffeine. How does it survive?

A 2015 study in Nature Communications found that the beetle relies on bacteria in its gut that break down caffeine. When researchers knocked out those bacteria with antibiotics, the beetles could no longer degrade caffeine; adding back a single strain of Pseudomonas bacteria restored the ability. It is a striking example of an evolutionary arms race: the plant builds a chemical shield, and a pest recruits microbes to get around it.

Why it matters for your cup

The caffeine in your coffee is the plant’s defense system, its tool for competing with neighbors and its way of making pollinators faithful. Caffeine is fairly stable during roasting, so much of what the plant put into its seeds ends up in your cup. Whether you choose an Arabica or a Robusta, you are tasting the result of millions of years of chemical evolution. To learn how caffeine then acts on your own body, see our article on the benefits of caffeine.

Taste the difference

Want to experience the high-caffeine side of the coffee family? Our Robusta from West Java, Indonesia, is a full-bodied medium roast with cacao, Brazil nut and malt notes and naturally more caffeine than Arabica. Our Max Caf Blend combines Tanzanian coffee with Indian Robusta for a bold, dark-cocoa cup made for long days. For a gentler cup, browse the Arabica coffees in our single origins.

FAQ: why plants make caffeine

Why do coffee plants produce caffeine?

Mainly as a defense against insects, and possibly to suppress competing plants. In low doses in nectar, caffeine also helps bees remember coffee flowers, which improves pollination.

Which other plants make caffeine?

Tea, cacao, yerba mate, guarana and several citrus species produce caffeine. Coffee, tea and cacao evolved the ability independently.

Does caffeine harm bees?

At the low levels found in nectar, caffeine boosted bees’ memory in the 2013 study. At high concentrations it is bitter to bees and repels them.

Why does Robusta have more caffeine than Arabica?

It is a different species with its own caffeine genes. A higher chemical defense may suit its warmer, lower-altitude habitats, but that link is a hypothesis.

Do insects ever become resistant to caffeine?

Yes. The coffee berry borer uses gut bacteria to break down caffeine, which lets it feed inside coffee seeds.

Sources

1. Nathanson J.A., “Caffeine and related methylxanthines: possible naturally occurring pesticides,” Science, 1984 (summarized by The Christian Science Monitor and NYBG). nybg.org
2. Friedman J., Waller G.R., “Seeds as allelopathic agents,” Journal of Chemical Ecology, 1983. link.springer.com
3. Wright G.A. et al., “Caffeine in floral nectar enhances a pollinator’s memory of reward,” Science, 2013; Newcastle University press release. ncl.ac.uk
4. Denoeud F. et al., “The coffee genome provides insight into the convergent evolution of caffeine biosynthesis,” Science, 2014. doi.org/10.1126/science.1255274
5. Zainuri et al., “The Chemical Characteristics of Arabica and Robusta Green Coffee Beans from Geopark Rinjani, Indonesia,” BIOTROPIA, 2023. journal.biotrop.org
6. Dessalegn Y. et al., “Genetic diversity and correlation of bean caffeine content with cup quality and green bean physical characteristics in coffee (Coffea arabica L.),” Journal of the Science of Food and Agriculture, 2008. PDF
7. Ceja-Navarro J.A. et al., “Gut microbiota mediate caffeine detoxification in the primary insect pest of coffee,” Nature Communications, 2015. PMC4510693

Facts checked in October 2026.

Keep reading: Benefits of caffeine · The best coffee beans in the world · Single origins collection