Nectar is a sugar solution that plants secrete from glands called nectaries, mostly to pay animals for carrying pollen. It is metered out a few microlitres at a time, because making it costs the plant carbon — and some plants produce it outside the flower entirely, to hire ants as bodyguards.
The useful way to think about nectar is as a wage. A plant that cannot move needs its pollen carried to another plant of the same species, and the cheapest way to arrange that is to pay something that can fly. What makes the arrangement interesting is that the payment is small on purpose. A flower does not fill up with nectar: it holds a sip, replenished slowly, because a visitor that drinks its fill would have no reason to go anywhere else — and going somewhere else is the entire point of the transaction. Nectar is also not only about pollination. Extrafloral nectaries, sitting on leaves and stems with no flower nearby, pay ants to patrol the plant and attack the insects eating it. And the composition is not simply sugar water: nectar carries amino acids, proteins and secondary compounds, some of them the same alkaloids the plant uses to defend itself, in quantities that appear to change which visitors come back.
Developed record · 46% complete · reviewed 2026-08-10
What this page covers
A plant secretion rather than an organism. Covers the flowering plants that produce it and the insects, birds, bats and mammals that drink it.
Quick facts
What it is
A secreted sugar solution, mostly sucrose, glucose and fructose
Concentration
Roughly 8% to over 70% sugar, depending on species
Typical volume
Often a few microlitres per flower, replenished slowly
Not only for pollinators
Extrafloral nectaries pay ants to defend the plant
Nectar is made on demand by specialised tissue, and there is less of it than people imagine.
Nectar is manufactured and metered out, because it costs the plant something
Established
Specialists would state this without hedging. Multiple independent lines of evidence agree.
Nectar is actively secreted by specialised glands, the nectaries, as an aqueous solution dominated by sucrose, glucose and fructose with amino acids, ions, proteins and secondary metabolites present in small quantities. Concentration ranges from roughly 8% to over 70% sugar depending on species and conditions. Secretion is regulated in volume and timing, and represents a measurable carbon cost.
Who this applies to
flowering plants producing floral or extrafloral nectar
Studied in
Angiospermae
You may have heard
“Flowers are full of nectar”
Most flowers hold a few microlitres, replenished slowly. Metering it out is the point: a flower that filled up would let one visitor drink its fill and leave, where a flower offering a sip sends the animal on to the next plant, which is the entire purpose of the transaction.
Why we rate it this way, and what the caveats are
EstablishedHigh confidence
Nectary anatomy, secretion dynamics and composition are directly measurable and have been for decades.
How far it can be extended
Nectary structure and secretion have been characterised across many families, though composition data are biased towards studied crops.
Caveats
Measured concentration depends strongly on humidity at the moment of sampling — nectar evaporates.
Composition data are patchy outside studied crops.
Secondary compounds in nectar are far less characterised than the sugars.
Still unanswered
How much do nectar secondary compounds shape which visitors return?
How large is the carbon cost of nectar relative to the rest of a flower?
Nectary structure and position, composition, concentration ranges and secretion dynamics.
Nectar comes from nectaries — patches of secretory tissue, usually at the base of the flower where a visitor has to push past the anthers to reach them. That position is not decorative. A nectary at the bottom of a tube forces an animal into contact with the reproductive parts on the way in and out, which is how a drink becomes a delivery.
The sugars are drawn from the plant’s phloem sap and modified: sucrose is often split into glucose and fructose, and water content is adjusted. Different families do this differently, which is why nectar concentration ranges from thin enough to lap to thick enough to be almost a syrup.
Concentration is not fixed even within a flower. Nectar evaporates, so the same flower is more dilute on a humid morning than on a dry afternoon — which is why field measurements have to record the weather to mean anything.
Words used here
Nectary
The gland that secretes nectar. Usually at the base of a flower; sometimes on leaves or stems instead.
Phloem
The tissue that carries sugars around a plant. The raw material nectar is made from.
By mass, nectar is water and three sugars. The ratio between sucrose and the two simple sugars varies systematically with who drinks it: hummingbird flowers tend towards sucrose-dominated nectar, many fly- and bat-visited flowers towards glucose and fructose. The pattern is real, and like all such patterns in pollination it is a tendency rather than a rule.
Sugars: sucrose, glucose and fructose, typically 8–70% by mass.
Amino acids, in small quantities but enough to matter for insects that live on nectar alone.
Proteins, including enzymes that alter the sugars after secretion.
Ions, principally potassium.
Secondary metabolites — alkaloids, phenolics — the same classes of compound plants use in defence.
That last item is the strange one. Nectar containing caffeine or nicotine is common, and the quantities are far too small to be nutritional. The current reading is that these compounds affect visitor behaviour — caffeine in nectar has been shown to improve how well bees remember a flower’s scent — but the evidence is thinner than the frequency with which the finding is repeated.
Nectar is not sterile. Yeasts and bacteria arrive on visitors’ mouthparts and grow in it, changing its sugar profile, its temperature and its scent before the next animal turns up.
Words used here
Secondary metabolite
A compound not required for basic growth — often defensive. Frequently present in nectar in trace amounts.
Nectar costs carbon that could have gone into seeds, so a plant that could achieve pollination without it would. Many do. Wind-pollinated plants — grasses, most trees of the northern forests, all the cereals — produce no nectar whatever, because there is nothing to pay. Their flowers are correspondingly plain: no petals worth the name, no scent, no colour.
Where animals are doing the carrying, the payment has to be enough to bring a visitor and not so much that it stays. This is the logic behind small volumes and slow replenishment. It also explains why a flower is often worth visiting again an hour later, and why foragers learn the timing.
And some plants take the arrangement further in the other direction. Roughly a third of orchid species offer nothing at all, attracting visitors by resembling a flower that pays, or by resembling something else entirely. Deception is a stable strategy where visitors cannot learn fast enough to avoid it.
Nectar feeds an enormous range of animals, and the differences between them shape the flowers they visit more than any other single factor.
Nectar drinkers and what they need from a flower
Group
What it needs
Consequence for the flower
Bees
Nectar for adults, pollen for larvae
Landing platforms, and pollen worth collecting as well as nectar
Butterflies and moths
Nectar reachable by a long coiled proboscis
Narrow tubes; night-scented pale flowers for moths
Hummingbirds and sunbirds
High energy, no landing site required
Tubular flowers, often held away from foliage, frequently sucrose-rich
Nectar-feeding bats
Large volumes, located in the dark
Big, robust, night-opening flowers with strong scent
Flies
Accessible nectar in small quantities
Open, shallow flowers; some smell of dung or carrion instead
Ants
Sugar, taken wherever it is offered
Usually poor pollinators — which is why many plants pay them outside the flower
Ants deserve the last row explained. They walk rather than fly, so they move pollen between flowers on the same plant rather than between plants, and their bodies carry antimicrobial secretions that damage pollen. A plant that wants ants generally wants them somewhere other than its flowers — which is exactly what extrafloral nectar arranges.
Extrafloral nectaries appear on the leaves or stems of thousands of plant species, including many acacias, cherries and passionflowers. The ants they attract patrol the plant and attack herbivores. It is nectar used as wages for defence rather than for transport.
Words used here
Extrafloral nectary
A nectary outside the flower, on a leaf or stem. Its usual function is attracting defensive insects, not pollinators.
Proboscis
The tubular mouthpart of a butterfly, moth or fly, used to reach nectar. Its length determines which flowers are usable.
Nectar is not sterile, and what lives in it changes who visits next.
Yeasts and bacteria arriving on pollinators ferment nectar and change who visits next
Well supported
Good evidence backs this, though some details remain open.
Nectar is routinely colonised by yeasts and bacteria transported on the mouthparts and bodies of flower visitors. Experimental inoculation of sterilised flowers alters nectar sugar composition and pH within days, and changes subsequent pollinator visitation: yeast-colonised flowers received more visits than bacterium-colonised flowers, and bacterial colonisation reduced visitation relative to sterile controls.
Who this applies to
one plant species with defined microbial inocula under field conditionsDo not extend this beyond the taxa listed — the popular version over-reaches.
Studied in
Mimulus aurantiacus, Metschnikowia reukaufii
You may have heard
“Nectar is a reward the plant provides”
It is a payment rather than a gift, and by the time an animal drinks it the plant no longer controls what is in it. Microorganisms delivered by earlier visitors have been altering the sugars, the acidity and the scent, which changes who comes next — a third party in an arrangement usually described as having two.
Why we rate it this way, and what the caveats are
Well supportedModerate confidence
A clean field manipulation with sterile and single-organism controls. Confidence is moderate because it is one plant species and visitation rather than seed set was measured.
How far it can be extended
Nectar microbial communities differ by plant, region and visitor assemblage, and the direction of the visitation effect depends on which organisms colonise.
Caveats
Sterilising a flower is itself a manipulation with effects beyond removing microbes.
Visitation was measured, so the consequence for the plant’s reproduction is inferred rather than shown.
Cultured inocula are simpler than the communities that assemble naturally.
Still unanswered
Does microbial colonisation change seed set, and in which direction?
Do plants exert any control over which microbes establish in their nectar?
Baseline nectar composition against which the microbial changes are measured.
Every visitor to a flower leaves something behind. Yeasts and bacteria travel on mouthparts and bodies, arrive in the nectar, and grow — and nectar is an excellent growth medium, being warm, wet and mostly sugar. Within a day or two of a flower opening, what is in the nectary is a fermenting community rather than a plant secretion.
How we know
Sterilising flowers and then deciding what lives in them
Nectar is full of yeasts and bacteria carried in by pollinators. Does that change anything for the plant?
Flowers were sterilised and then inoculated with a defined treatment — a nectar yeast, a nectar bacterium, both, or nothing — and returned to a wild population where pollinators visited freely. Because every flower was otherwise identical and the microbial treatment was the only difference, any change in nectar chemistry or in visitation is attributable to the organisms present.
What happened
Microbial colonisation changed nectar sugar composition and pH within days. Flowers colonised by yeast received more pollinator visits than those colonised by bacteria, and bacterial colonisation reduced visitation relative to sterile flowers.
What it shows
That there is a third party in an interaction usually described as having two. The plant produces the nectar and does not control what it has become by the time an animal arrives, because previous visitors delivered the organisms now fermenting it.
What it does not show
Visitation is not seed set, so what this costs or gains the plant reproductively is inferred rather than measured. One plant species with cultured inocula is simpler than the communities that assemble in the wild. And sterilising a flower is itself a manipulation with effects beyond removing microbes.
The controls — what makes this evidence rather than a story
Sterile flowers processed identically, which distinguishes the effect of the microbes from the effect of being handled and sterilised.
Single-organism inocula as well as the mixture, so a combined effect can be separated into contributions.
Nectar chemistry measured directly rather than inferred from visitation.
Wild pollinators making free choices among treatments in a natural setting, rather than a captive preference assay.
The consequence worth holding onto is what it does to the usual account of pollination. A plant makes nectar to pay visitors, and by the time a visitor drinks it the plant no longer controls what it is paying with: the sugars have been altered, the acidity has shifted, and in some cases the temperature has risen from microbial activity. Whether that helps or harms depends on which organism happened to arrive, which nothing in the arrangement decides.
Yeast-colonised flowers in one field experiment received more pollinator visits than bacterium-colonised ones, and bacterial colonisation reduced visits below the sterile baseline. The same flower, the same nectar, different microbes.
Words used here
Nectar microbiome
The community of yeasts and bacteria living in nectar, delivered largely by flower visitors themselves.
Biting a hole in a flower to steal nectar sometimes benefits the flower
Well supported
Good evidence backs this, though some details remain open.
Nectar robbers extract nectar through a perforation in the corolla, bypassing anthers and stigma. Measured effects on plant reproductive output range from strongly negative through neutral to positive: where robbing depletes nectar, legitimate visitors travel further between plants, which can increase outcrossing and offset or exceed the direct loss.
Who this applies to
systems where robbing and seed set have both been measuredDo not extend this beyond the taxa listed — the popular version over-reaches.
Studied in
Bombus, Angiospermae
You may have heard
“Nectar robbers are cheats harming the plant”
The behaviour looks like cheating and its consequences are not fixed. Sorting interactions into mutualism and parasitism by how they look is exactly what this case defeats — the only way to know is to count the seeds.
Why we rate it this way, and what the caveats are
Well supportedModerate confidence
The behaviour and its variable consequences are documented across many systems. Confidence is moderate because outcomes are strongly context-dependent and often measured over one season.
How far it can be extended
The direction of the effect depends on the plant, the robber, the legitimate visitors and their density, and cannot be predicted from the behaviour alone.
Caveats
The systems studied are unlikely to be a random sample of those that exist.
Single-season measurements may miss effects on the plant over its lifetime.
Secondary robbers using existing holes complicate attribution.
Still unanswered
What predicts whether robbing will be costly or beneficial in a given system?
Irwin et al., 2010 · Annual Review of Ecology, Evolution, and Systematics
Synthesis of measured effects on seed set, including the outcrossing mechanism behind positive outcomes.
A bumblebee with mandibles strong enough to bite through a corolla can reach nectar in a flower far too long for its tongue, by making a hole at the base and drinking through it. Once the hole exists, other insects use it — including honey bees, which mostly cannot make one.
The obvious conclusion is that this harms the plant, and sometimes it does. But depleted flowers send legitimate visitors further afield, and a pollinator that travels further carries pollen between more distant plants, which raises outcrossing. In some measured systems the net effect on seed set is neutral; in a few it is positive.
This is the reason NatureHQ resists sorting interactions into helpful and harmful by how they look. The behaviour is identical in every case. The outcome is a measurement, and it comes out differently in different places.
Words used here
Nectar robbing
Taking nectar through a hole in the side of a flower, bypassing the anthers and stigma entirely.
Outcrossing
Fertilisation between two different plants rather than within one. Generally produces more variable offspring.
What are the trace compounds in nectar actually doing?
Why it matters: Caffeine, nicotine and various alkaloids turn up in nectar at concentrations too low to feed anything. The behavioural effects reported are interesting and the evidence is thinner than the frequency of citation suggests.
How much do nectar microbes change what a visitor experiences?
Why it matters: Yeasts growing in nectar alter its sugars, scent and even temperature. Whether this materially changes pollination outcomes is largely unmeasured.
What fraction of a plant’s carbon budget does nectar represent?
Why it matters: The cost of nectar is the premise of almost every argument about why flowers are the way they are, and it has been measured in remarkably few species.