When we think of nectar, most of us picture delicate blossoms brimming with sugary liquid designed to lure bees, butterflies, and hummingbirds. But not all nectar is born from flowers. Around 4,000 plant species worldwide have evolved secretory glands called extrafloral nectaries, which release nectar on stems, leaves, or branches rather than inside flowers. Unlike floral nectar, this sweet offering is not meant to attract pollinators—it’s designed to recruit defenders.
By offering sugary bribes, plants entice ants and other protective insects. In return for the nectar, these small but fierce allies patrol the plant, driving away hungry herbivores such as caterpillars and beetles. At first glance, this seems like a win-win: the plant gains protection, and the ants gain food. But in ecology, balance is rarely simple. A closer look reveals that this partnership sometimes comes at a hidden cost.
When Defenders Become Disruptors
A recent study published in the Journal of Ecology uncovered a fascinating twist in the story of extrafloral nectaries. While ants are excellent bodyguards, their presence can disrupt another vital relationship: pollination.
Pollinators, especially bees, are essential for plant reproduction. But when extrafloral nectaries are located too close to flowers, ants tend to linger nearby. Bees, which must crawl deep into blossoms to collect nectar and pollen, are vulnerable to ant harassment. The result? Bees cut their visits short or avoid the flowers altogether.
As Amanda Vieira da Silva, lead author of the study and researcher at the Federal University of ABC in Brazil, explains:
“Bees need to get very close to the flower to collect pollen and floral nectar, but ants don’t allow them to stay for long. Not surprisingly, our analysis showed that the presence of ants is detrimental to pollination when extrafloral nectaries are close to flowers.”
In other words, the very guards recruited to defend the plant can unintentionally block its reproductive lifeline.
Butterflies Break the Rules
Interestingly, not all pollinators are equally affected. Butterflies appear to navigate this ant-guarded world with ease. Unlike bees, butterflies sip nectar using their long, straw-like proboscis, allowing them to feed from a safe distance without confronting ants face-to-face.
This difference highlights how the feeding strategies of pollinators shape the outcome of plant–ant–pollinator interactions. For plants, the identity of their pollinators matters just as much as the presence of defenders.
Distance Makes the Difference
Not all extrafloral nectaries spell trouble. The study, which analyzed data from 27 empirical studies out of an initial 567, found that plants with nectaries located on leaves, stems, or branches—away from the flowers—actually fared better. In these cases, ants still provided protection from herbivores, but without interfering with pollination. As a result, these plants enjoyed greater reproductive success.
This delicate spatial balance shows how finely tuned evolutionary strategies can be. Where a gland is placed on a plant can tip the scales between success and failure in reproduction.
Evolution’s Push and Pull
Extrafloral nectaries are not fixed traits; they are remarkably flexible in evolutionary terms. Analyses show that plants can gain or lose these glands over time, depending on whether they provide an advantage or a burden.
If ants consistently scare away bees and reduce pollination, natural selection may favor plants that lose their nectaries. Conversely, if the benefits of defense outweigh the costs, nectaries are more likely to be retained. This evolutionary balancing act has shaped the diversity we see today.
Notably, of the nearly 1,000 plant genera with extrafloral nectaries, only 46 rely exclusively on bees for pollination. This striking pattern suggests that plants depending heavily on bees may have been more likely to shed nectaries over evolutionary time, avoiding the costly conflict between defenders and pollinators.
A Dance of Multiple Partnerships
Plants rarely interact with just one partner species. Instead, they live in networks of relationships that overlap and intertwine. Ants, bees, butterflies, and even microbes can all influence a plant’s fate.
Laura Carolina Leal, co-author of the study and professor at the Federal University of São Paulo, explains:
“Studies have typically focused on the effect of only one isolated interaction on plants. But these interactions can occur at the same time. To understand how they influence plant growth and reproduction, we need to look at them in an integrated way.”
This idea—known as multiple mutualisms—recognizes that plants often juggle several beneficial partnerships simultaneously. For example, legumes with extrafloral nectaries not only feed ants but also host nitrogen-fixing bacteria in their roots. These microbes enrich the soil, boosting plant productivity and potentially allowing plants to invest in resources for both pollinators and defenders.
Avoiding Conflict Through Timing
Nature also finds creative ways to sidestep conflicts. Some plants produce flowers and extrafloral nectaries at different times of the year. By separating the periods when they need pollinators from those when they need defenders, these plants reduce the chance of interference.
This seasonal strategy reflects a larger truth: evolution doesn’t aim for perfection, but for workable compromises that allow species to survive and reproduce under changing conditions.
Why This Matters
The hidden drama between plants, ants, and pollinators might seem like an esoteric detail of ecology, but its implications are profound. Pollination underpins global food security, biodiversity, and ecosystem stability. Understanding how different interactions shape pollination helps us predict how ecosystems will respond to disturbances such as habitat loss, climate change, or declines in pollinator populations.
It also reminds us of an essential ecological lesson: no relationship exists in isolation. Every plant and animal is part of a web of interactions, where small changes ripple outward in unexpected ways. What begins as a drop of nectar on a leaf can reshape the fate of flowers, pollinators, and even evolutionary lineages.
The Endless Web of Life
Extrafloral nectaries illustrate the complexity of nature’s designs. They are not simply sugar taps for ants but strategic investments, balancing protection and reproduction. Sometimes they help, sometimes they hinder, but always they reveal the delicate negotiations at the heart of life.
As ecologist Anselmo Nogueira, another co-author of the study, puts it:
“If the resource is very good for the bee in the flower and for the ant on the leaf, perhaps they’ll never meet.”
It is a poetic reminder that life thrives not by avoiding conflict altogether but by weaving a tapestry of compromises, timing, and adaptations.
In the end, the story of extrafloral nectaries is not just about plants, ants, and bees. It is about the dance of relationships that sustains our world—a dance as fragile as nectar and as enduring as evolution itself.
More information: Amanda Vieira da Silva et al, Ants on flowers: Protective ants impose a low but variable cost to pollination, moderated by location of extrafloral nectaries and type of flower visitor, Journal of Ecology (2025). DOI: 10.1111/1365-2745.70087
