Most ants never have sex, but the ones that do make it count. In a typical colony of thousands or even millions of individuals, only a tiny fraction are reproductively active. The sterile workers you see marching across your kitchen floor will never mate. Sex is reserved for winged queens and males, produced specifically for reproduction, and their single mating event shapes the genetic fate of a colony that can persist for decades. The biology behind how ants reproduce is stranger and more varied than most people realize.
Who Actually Mates in an Ant Colony
An ant colony is built around a division of labor so extreme that most members have given up reproduction entirely. The vast majority of ants in any colony are sterile female workers. They forage, defend the nest, tend larvae, and manage waste, but they do not mate. Reproduction falls to two specialized castes: queens (fertile females) and males. Queens are typically larger than workers and are born with wings. Males are also winged and exist for essentially one purpose: to mate with a queen. After fulfilling that role, males die within hours or days.
This setup means that sex in ants is not a recurring activity the way it is for many animals. A queen mates once in her life, during a brief window, and then relies on stored sperm for every egg she will ever fertilize. Males never work, never forage, and contribute nothing to colony life beyond their genetic material. The entire reproductive output of a colony funnels through the queen’s body, using sperm she collected during a single mating event that may have lasted only minutes.
The Nuptial Flight
The main event in ant reproduction is the nuptial flight, a synchronized mass mating event in which winged queens and males from many colonies take to the air at the same time. If you have ever seen swarms of flying ants on a warm summer day, you were watching a nuptial flight in progress. These events are triggered by weather conditions, though the details vary by species. Research on European ant species found that air temperature, humidity, wind speed, and time of day all played a role, with low wind speeds being a consistent requirement during summer flights.1PubMed. Weather conditions during nuptial flights of four European ant species Interestingly, a study that used airport bird-strike samples from swifts to track when ants were flying found that environmental variables alone did not fully explain the timing, suggesting that internal colony-level readiness also matters.2PubMed Central. Opportunistic airport-collision samples from swifts reveal ant nuptial flight phenology
During the flight, a queen may mate with one male or several, depending on the species. She collects and stores sperm internally, then lands, sheds her wings, and begins searching for a place to start a new colony. Males, having served their purpose, typically die shortly after mating. The nuptial flight is both the beginning and the end of sexual activity for every ant involved.
How Sex Determines Whether an Ant Is Male or Female
Ant sex determination works nothing like it does in humans. Instead of sex chromosomes, ants use a system where fertilized eggs become female and unfertilized eggs become male. This means males develop from eggs that were never touched by sperm. They carry only their mother’s genetic contribution and have half the usual number of chromosomes. Females, produced from fertilized eggs, carry a full set. This system, shared with bees and wasps, is called haplodiploidy.3PubMed. The doublesex gene integrates multi-locus complementary sex determination signals in the Japanese ant, Vollenhovia emeryi
The mechanism that makes this work involves specific genetic loci where diversity matters. When a fertilized egg carries two different versions of the gene at a sex-determination locus, it develops as a female. When it carries two identical copies, or only one copy because the egg was unfertilized, it develops as a male. Research on the clonal raider ant identified a candidate locus of about 46,000 base pairs where all females were found to carry two different alleles, while most diploid males were homozygous.4PubMed Central. Heterozygosity at a conserved candidate sex determination locus is associated with female development in the clonal raider ant (Ooceraea biroi) This has a practical consequence: inbreeding, which increases the chance of an egg getting two identical copies, can produce diploid males, which are essentially genetic dead weight for a colony because they are often sterile or inviable.
A queen decides the sex of her offspring in a remarkably direct way. She controls whether or not to release sperm from her internal storage organ as each egg passes through her reproductive tract. Fertilized eggs become female workers or new queens; unfertilized eggs become males. The ratio of males to females a colony produces is therefore partly under the queen’s control, though workers can also influence the outcome by selectively destroying eggs or larvae of the unwanted sex.
Why Queens and Workers Fight Over Sex Ratios
Because of the unusual genetics of haplodiploidy, queens and workers have different preferences for how many males versus new queens the colony should produce. Workers are more closely related to their sisters than to their brothers, which means they genetically “prefer” the colony to invest more in producing new queens. The queen, equally related to sons and daughters, favors a more balanced ratio. This leads to a genuine conflict of interest within the colony.
Studies have documented this tug-of-war in real colonies. In the ant Leptothorax acervorum, researchers found that the number of queens and workers in a colony predicted the ratio of new workers to new queens being produced, consistent with queen-worker conflict over caste determination.5PubMed. Queen-Worker Conflict over Sexual Production and Colony Maintenance in Perennial Social Insects In Formica pratensis wood ants, the conflict played out seasonally: later broods were more female-biased over a three-year sampling period, matching predictions about workers skewing investment toward their preferred sex.6PubMed. Sex allocation conflict between queens and workers in Formica pratensis wood ants predicts seasonal sex ratio variation Workers cannot lay fertilized eggs themselves, but they can destroy male eggs laid by the queen or preferentially feed female larvae, tilting the colony’s reproductive output toward sisters they are more related to.
Males Are Disposable, and Their Biology Reflects It
Male ants are built to mate and die. They do not forage, they do not defend the nest, and in most species, they are not even fed by workers once they become adults. Their sole contribution to the colony is genetic, and their bodies reflect this narrow purpose. One striking feature is that males finish producing sperm before they even emerge as adults. In the ant Crematogaster osakensis, sperm production is complete by the time the male ecloses from its pupal case, and the testes begin to shrink within ten days.7PubMed. Journey of sperms from production by males to storage by queens in Crematogaster osakensis Males of the genus Cardiocondyla similarly stop producing sperm during the late pupal stage.8PubMed. Fighting for a harem of queens: physiology of reproduction in Cardiocondyla male ants
This means every male ant enters adult life with all the sperm he will ever have. He cannot replenish his supply. The total number of sperm stored at emergence is essentially his entire reproductive budget, and research on desert ants confirmed this is a reliable measure of a male’s total investment in reproduction.9Functional Ecology. Sperm production characteristics vary with level of sperm competition in Cataglyphis desert ants Species where queens mate with multiple males tend to produce males with more sperm, a predictable arms race driven by competition.
Frequent mating shortens a male’s already brief life. In Cardiocondyla obscurior, males that mated frequently lived shorter lives than those that mated infrequently or remained virgins. But the trade-off was clearly worth it from an evolutionary perspective: inseminating as many queens as possible maximized their genetic legacy, even at the cost of dying sooner.10PubMed Central. Mating and longevity in ant males
How Queens Store Sperm for Decades
After her single mating flight, a queen must make the sperm she collected last for the rest of her reproductive life, which in some species spans 20 to 30 years. She stores sperm in a specialized organ called the spermatheca, and the conditions inside it are engineered to keep sperm alive and functional for extraordinarily long periods.
Research has revealed that the interior of the spermatheca is kept in a state of near-zero oxygen. In two ant species from different subfamilies, oxygen levels inside the sperm storage organ were extremely low, suggesting this is a widespread feature across ants rather than a quirk of one lineage.11Scientific Reports. Near-anoxia induces immobilization and sustains viability of sperm stored in ant queens The near-absence of oxygen immobilizes the sperm, which sounds counterintuitive but serves two protective functions. Immobile sperm produce fewer reactive oxygen species, the damaging byproducts of normal metabolism, and they avoid physical wear from unnecessary movement. The researchers confirmed that artificially creating low-oxygen conditions also immobilized sperm and helped maintain their viability.
Preparing the spermatheca for this long-term storage role begins before the queen even mates. In Crematogaster osakensis, the near-anoxic conditions and elevated pH inside the spermatheca were already established about eight days after the queen emerged as an adult, well ahead of the nuptial flight. Morphological changes in the organ’s lining, thought to help clear waste from stored sperm, were then triggered by the mating flight itself.12PubMed. Physiological and morphological development of the spermatheca in queens of the ant Crematogaster osakensis The queen’s body essentially builds the storage facility in two stages: the chemical environment first, the maintenance infrastructure after mating.
The Chemical Battle Between Queen and Male
Mating in ants is not a perfectly cooperative exchange. The fluids that accompany sperm and the fluids inside the queen’s spermatheca are in biochemical conflict. Research on ant seminal fluid found that it contains proteins capable of harming rival sperm, an adaptation that makes sense when a queen mates with multiple males. But the queen’s spermathecal fluid fights back: it targets a small fraction of the seminal fluid’s proteins for breakdown, including enzymes that would otherwise damage competing sperm. Exposure to the queen’s fluid reduced the ability of seminal fluid to harm rival sperm within hours.13ScienceDirect. Protein-Level Interactions as Mediators of Sexual Conflict in Ants
This makes evolutionary sense from the queen’s perspective. If she has mated with several males, she benefits from keeping as much viable sperm as possible, giving her a larger genetic toolkit for producing diverse offspring. The male, on the other hand, benefits from his sperm outcompeting rivals. The queen’s body acts as a mediator in this conflict, chemically disarming the weapons males deploy against each other’s sperm.
How the Queen Keeps Workers Sterile
Workers are female and have ovaries, so in principle, they could lay eggs. In practice, the queen suppresses worker reproduction using chemical signals. These queen pheromones are remarkably consistent across social insects. Research found that wasps, ants, and some bees all use similar classes of chemical compounds, specifically saturated hydrocarbons on the body surface, to signal fertility and suppress worker reproduction.14PubMed. Conserved class of queen pheromones stops social insect workers from reproducing In at least one ant species, a specific compound inhibited ovarian development in workers and reduced aggression toward objects coated with it.15PubMed Central. Queen pheromones: The chemical crown governing insect social life
When the queen dies and her pheromone signal fades, workers in some species begin developing their own ovaries and laying unfertilized eggs. Since workers cannot mate, these eggs can only produce males. This is a last-ditch reproductive effort: with no queen to produce the next generation of workers, the colony is doomed, so workers shift to producing sons as a way to pass on at least some of their genes before the colony collapses.
When Workers Take Over Reproduction
Not all queenless colonies are dying. Some ant species have evolved a system where certain workers, called gamergates, take on the reproductive role permanently. These mated workers function as queens and can produce both male and female offspring. In the queenless ant Diacamma ceylonense, the worker destined to become the colony’s gamergate behaves very aggressively toward her nestmates during the first days of adult life. This aggression fades after about three weeks, once she begins laying eggs and is ready to mate.16PubMed Central. Regulation of reproduction in a queenless ant: aggression, pheromones and reduction in conflict The transition from aggressive dominance-establishment to settled reproduction mirrors, in a compressed timeline, the kind of power dynamics seen in many animal societies.
Ants That Skip Sex Entirely
Some ant species have abandoned sexual reproduction altogether. The fungus-gardening ant Mycocepurus smithii reproduces through a form of cloning called thelytokous parthenogenesis, in which queens produce female offspring from unfertilized eggs. Examination of queens from this species found completely empty spermathecae alongside well-developed ovaries and clear evidence of active egg-laying, confirming they reproduced without any sperm at all.17PLoS ONE. Thelytokous Parthenogenesis in the Fungus-Gardening Ant Mycocepurus smithii (Hymenoptera: Formicidae) Males have never been found in this species. Every individual is a genetic clone, or near-clone, of the queen.
This raises an obvious question: without genetic mixing from sex, how does the species cope with parasites and changing environments? For now, M. smithii appears to be doing fine, but asexual lineages in many organisms tend to be evolutionary dead ends over long timescales. The species may be young enough that the costs of genetic uniformity have not yet caught up with it, or its symbiotic relationship with the fungus it farms may buffer it in ways we do not fully understand.
Hybridogenesis and Other Exotic Mating Systems
Between straightforward sex and complete cloning, some ant species have evolved mating systems that are genuinely bizarre. In dependent-lineage populations of harvester ants, two genetically distinct lineages coexist and interbreed, but the offspring of those matings are always sterile workers. Queens can only be produced from matings within the same lineage.18PubMed. Male parentage in dependent-lineage populations of the harvester ant Pogonomyrmex barbatus This means a queen must mate with males from both lineages: same-lineage mates to produce her replacement queens, and different-lineage mates to produce her workforce.
The same pattern appears in the Mediterranean harvester ant Messor barbarus, where all new queens arose from within-lineage matings while all workers came from between-lineage crosses.19PubMed Central. Cryptic lineages hybridize for worker production in the harvester ant Messor barbarus This system locks the two lineages into mutual dependence: neither can produce a complete colony without the other. It also means that whether a fertilized egg becomes a queen or a worker is determined genetically by the combination of lineages in the cross, rather than by nutrition or other environmental cues that control caste in most ant species.
A related pattern appears in the desert ant Cataglyphis hispanica, where genetic caste determination has been documented directly. In this species, hybrid eggs from interlineage matings always develop into workers, while same-lineage eggs develop into queens. Non-hybrid eggs have apparently lost the ability to develop as workers entirely.20Journal of Evolutionary Biology. Genetic determination of female castes in a hybridogenetic desert ant
Polyandry and the Genetics of Remating
In many ant species, queens mate with only one male. But in others, queens mate with several, a strategy called polyandry. The fire ant Solenopsis invicta reveals how genetics can drive this decision. Whether a queen mates once or multiple times depends on the genotype of her first mate. Queens mated to males carrying one variant of a gene complex called Gp-9 remained highly receptive to additional mating, while queens mated to males carrying a different variant rarely remated. The difference appears linked to sperm count: males with the variant associated with polyandry had fewer sperm, which may serve as a signal to the queen that she needs more.21PubMed Central. Male reproductive fitness and queen polyandry are linked to variation in the supergene Gp-9 in the fire ant Solenopsis invicta
Polyandry benefits the colony by increasing genetic diversity among workers, which can improve disease resistance and division of labor. But it creates tension: each additional male’s sperm dilutes the genetic contribution of previous mates, setting up competition among unrelated patrilines within the same colony.
Inbreeding as a Strategy
Most ant species avoid inbreeding because of the diploid-male problem described earlier. But some species have turned inbreeding into a deliberate strategy. The invasive ant Brachyponera chinensis routinely mates between siblings, with queens mating with their own brothers. This is not a consequence of small population sizes during invasion but a pre-existing behavior observed in their native range.22PubMed. Inbreeding tolerance as a pre-adapted trait for invasion success in the invasive ant Brachyponera chinensis The tolerance for inbreeding may have helped the species survive the genetic bottlenecks that typically devastate invasive populations, giving it an edge over competitors that depend on outbreeding.
What Happens After Mating
Once a queen lands after her nuptial flight, she faces the most dangerous period of her life. She must find a suitable nest site, often digging a small chamber alone, and then seal herself inside to raise her first batch of workers using only the energy reserves stored in her body. In most ant species, the queen does not eat during this period. She metabolizes her now-useless flight muscles and fat stores to nourish herself and feed the first larvae. This fully claustral founding strategy means the queen is entirely self-sufficient until her first workers emerge and begin foraging.
Not all species follow this pattern. The seed-harvester ant Pogonomyrmex californicus uses an unusual strategy where the queen must actually leave the nest to forage during the founding period. Compared to related species that stay sealed underground, P. californicus queens carry less body fat but produce significantly more and heavier first-brood workers, because foraging provides extra energy beyond what body reserves alone could supply.23PubMed. Semi-claustral colony founding in the seed-harvester ant Pogonomyrmex californicus: a comparative analysis of colony founding strategies The trade-off is risk: a foraging queen is exposed to predators and environmental hazards that a sealed queen avoids.
Parasites That Hijack Ant Reproduction
Ant reproduction is not only shaped by the ants themselves. Wolbachia, a bacterium that infects a huge fraction of insect species, can manipulate the sex ratios of ant colonies. In an experiment involving artificial selection on caste ratios, colonies infected with Wolbachia produced a higher proportion of females compared to uninfected colonies, with a roughly 13-percentage-point increase in the proportion of female offspring.24Journal of Evolutionary Biology. Artificial selection on ant female caste ratio uncovers a link between female‐biased sex ratios and infection by Wolbachia endosymbionts Since Wolbachia is transmitted through eggs and not sperm, it benefits the bacterium to skew reproduction toward females, who will pass the infection to the next generation.
Other parasites operate at the colony level rather than the cellular level. Queens of the slave-making ant Polyergus breviceps cannot rear their own brood at all. Instead, a newly mated Polyergus queen must invade a colony of a different species, kill the resident queen, and trick the host workers into raising her offspring.25Animal Behaviour. Colony takeover by a socially parasitic ant, Polyergus breviceps: the role of chemicals obtained during host-queen killing The parasitic queen acquires chemical cues from the dead host queen that help her gain acceptance from the orphaned workers. The host workers then raise the parasite’s offspring as if they were their own, and the cycle continues when those offspring raid neighboring host colonies for more workers.
Artificial Light and the Future of Nuptial Flights
The synchronized nuptial flights that drive ant reproduction are sensitive to environmental conditions, and human activity is beginning to interfere. Artificial light at night disrupts the activity patterns of nocturnal and crepuscular ant species, forcing some to curtail their activity and causing others to misjudge safe foraging and dispersal windows.26IntechOpen. Architects in the Dark: Nocturnal Behavior and Evolutionary Trade-Offs in Social Insects For species whose nuptial flights happen at dusk or dawn, light pollution could interfere with the timing cues that coordinate these mass events. The effect is likely subtle and hard to measure at the population level, but given that a failed nuptial flight means zero reproduction for every queen and male involved, even modest disruptions could have outsized consequences for local populations over time.