A colony, in biology, is a group of organisms of the same species living in close physical association, often with some degree of cooperation, shared resources, or division of labor. That sounds tidy, but the word stretches across an enormous range of life forms. A bacterial smear on an agar plate, a honeybee hive, a coral reef, a seabird nesting cliff, and a grove of genetically identical aspen trees are all called colonies, even though what connects the members in each case differs dramatically. The reason one term covers so many arrangements has as much to do with linguistic history as with biology, and the tensions built into the word reveal genuine scientific debates about where an individual ends and a group begins.
Where the Word Came From
The biological use of “colony” is borrowed from human political language. The Latin colonia originally described Roman settlements established in newly conquered territory, and traces further back to colonus, meaning a tenant farmer or settler in a new land. As European empires expanded in the late sixteenth century, the word migrated into natural history to describe a group of animals of the same kind that establishes itself in a particular locality. That migration was not accidental: early naturalists often projected the social structures they knew onto the organisms they observed, framing bee hives and coral reefs through the lens of human settlement. The imperial connotations embedded in the word have drawn recent scholarly criticism, with some researchers arguing that the terminology carries assumptions about hierarchy and conquest that may not apply to the organisms in question.
Insect Colonies and the Superorganism Idea
When most people hear “colony,” they picture ants, bees, or termites. These are eusocial insects, species in which a reproductive division of labor is so extreme that most individuals never breed. Instead, workers perform tasks like foraging, nest defense, and brood care, while one or a few queens handle reproduction. In carpenter ants, for example, morphologically distinct worker castes called minors and majors show pronounced differences in foraging and scouting behavior, with epigenetic processes like histone modification helping to regulate which caste a given ant falls into.1PubMed Central. Epigenetic (re)programming of caste-specific behavior in the ant Camponotus floridanus The colony, in this sense, is not just a bunch of ants living near one another. It is a functional unit with specialized parts, much the way a body has specialized organs.
This is why researchers sometimes call insect colonies “superorganisms.” The term captures the idea that colony-level function emerges from the interactions of relatively less capable individuals, none of whom has a complete picture of the colony’s situation.2PubMed. The Psychology of Superorganisms: Collective Decision Making by Insect Societies A single ant cannot weigh all the options available to the group, but the colony as a whole can reach decisions that account for the full set of choices. Research on house-hunting ants has shown that collective comparisons emerge from the interactions of poorly informed individuals, with the colony arriving at conclusions that are evident only at the group scale.3PubMed Central. How collective comparisons emerge without individual comparisons of the options Weaver ants, likewise, collectively modulate their investment in bridge-building chains based on simple distance rules followed by individual ants, with no need for any ant to understand the overall engineering problem.4PubMed Central. A simple mechanism for collective decision-making in the absence of payoff information
This kind of colony challenges the everyday assumption that a colony is merely a gathering. The individual ant is alive and autonomous in a narrow sense, but it cannot survive or reproduce alone. The colony is the unit that reproduces, competes, and adapts. Whether that makes the colony itself an “individual” in the biological sense is a question philosophers and biologists continue to debate.5PubMed Central. Can’t see the colony for the bees: behavioural perspectives of biological individuality
Marine Colonies Where “Individual” Gets Blurry
Insect colonies are at least made up of organisms you can pick up with tweezers and identify as separate animals. In many marine invertebrates, the boundary between colony member and colony is far harder to draw. Siphonophores are pelagic relatives of jellyfish in which the colony is composed of polyps and medusae that are each homologous to free-living animals but remain physically attached because the asexual budding process that produces them is incomplete. These zooids are physiologically integrated and functionally specialized for different tasks, precisely organized within the colony.6Systematic Biology. Molecular Phylogenetics of the Siphonophora (Cnidaria), with Implications for the Evolution of Functional Specialization Gene expression analysis confirms that different zooid types within a siphonophore colony show strikingly distinct patterns, reflecting their separate anatomies and functions.7Molecular Biology and Evolution. Evolution of Gene Expression across Species and Specialized Zooids in Siphonophora
Is a siphonophore one animal or many? The zooids cannot survive alone, and they share a circulatory system. But each zooid has its own developmental origin and its own body plan. The answer depends on which definition of “individual” you choose, and the fact that the question resists a clean answer is part of why biologists find colonial organisms so fascinating.
Corals present a related puzzle. Reef-building corals are colonial cnidarians whose survival depends on the coordinated growth of thousands of interconnected polyps.8bioRxiv. Comparative 3D analysis reveals species-specific patterns of coral polyp morphology and gastrovascular integration In some species, internal tissue networks connect not just neighboring polyps but distant ones, enabling resource sharing across the colony. The coral Lobophyllia is an interesting edge case: its adult polyps physically separate from one another and lack connecting tissue, yet they still transfer photosynthetic products to injured neighbors, behaving like a colony in terms of energy cooperation even though they look like solitary animals.9Journal of Experimental Biology. Energy integration between the solitary polyps of the clonal coral Lobophyllia corymbosa
Bryozoans add another wrinkle. These tiny marine animals grow colonies by budding new physiologically connected zooids from a founding individual. In some species, zooids come in dramatically different shapes: feeding autozooids, beak-shaped avicularia that snap at small predators, and branching rhizoids that anchor the colony.10PubMed Central. Differential Gene Expression Between Polymorphic Zooids of the Marine Bryozoan Bugulina stolonifera You might expect that more zooid types means tighter physiological connections, but a comparison of two encrusting bryozoan species found the opposite: the species with more zooid polymorphism actually had fewer pore connections per zooid than a monomorphic species.11PubMed. Does polymorphism predict physiological connectedness? A test using two encrusting bryozoans Colonial integration, it turns out, is not a single dial that turns up uniformly. Different aspects of coloniality, like specialization and physical connectivity, can evolve independently.
Microbial Colonies and Biofilms
At the smallest scale, the word “colony” describes a visible cluster of bacteria or other microorganisms growing on a surface. In a laboratory, a single bacterium deposited on an agar plate divides repeatedly to form a circular mound of millions of genetically identical cells. This is the colony in its most stripped-down sense: organisms of the same species, in one place, descended from one founder.
But even this simple-sounding arrangement involves cooperation. Many bacteria produce an extracellular matrix made of proteins, polysaccharides, and DNA that holds the colony together into a structured biofilm.12PubMed Central. Bacterial extracellular matrix as a natural source of biotechnologically multivalent materials These biofilms are not just passive clumps; they are viscoelastic gels whose matrix composition influences the colony’s expansion rate and overall shape.13PubMed Central. The role of biofilm matrix composition in controlling colony expansion and morphology The cells within a biofilm also communicate. Through a process called quorum sensing, bacteria release signal molecules into their environment; as the population grows, the concentration of these molecules rises until a threshold triggers coordinated changes in gene expression across the colony.14PubMed. Quorum sensing as a population-density-dependent determinant of bacterial physiology The colony, in effect, senses its own density and adjusts its behavior accordingly.
Biofilm colonies have enormous practical consequences. Bacteria growing in biofilm mode can be up to a thousand times more resistant to antibiotics than the same cells floating freely, which is a major reason infections associated with medical implants are so difficult to treat.15PubMed Central. Mechanisms and Control Strategies of Antibiotic Resistance in Pathological Biofilms The resistance mechanisms at work in biofilms are different from those that make individual bacteria drug-resistant. Rather than relying on mutations in single cells, biofilm resistance depends on multicellular strategies: the matrix physically blocks drug penetration, cells in the interior enter dormant states, and signaling between neighbors coordinates defensive responses.16The Lancet. Antibiotic resistance of biofilms In this respect, the bacterial colony behaves less like a heap of independent cells and more like a tissue with emergent group-level properties.
Clonal Colonies in Plants and Fungi
Plants and fungi use the word “colony” in yet another way: to describe a group of genetically identical individuals produced by vegetative reproduction. A stand of aspen trees connected by a shared root system is a single clone, sometimes covering enormous areas. The most famous example, Pando in Utah, consists of tens of thousands of stems that are all genetic copies of one original tree. Each trunk looks and acts like a separate tree, but underground they are one interconnected organism, or one colony, depending on your definition.
Fungal colonies stretch the concept further. Filamentous fungi grow as networks of thread-like hyphae that branch and fuse, creating a continuous web of cytoplasm called a mycelium. This network can transport nutrients over long distances without needing anything like a circulatory system.17PubMed Central. Physiological significance of network organization in fungi Experiments with Neurospora crassa mutants that cannot form proper networks showed that nutrient translocation suffers in both uniform and patchy environments, confirming that the interconnected network structure is not incidental but functionally important.18PubMed Central. Physiological significance of network organization in fungi Some woodland fungi can even reorganize their networks to maintain high transport capacity and robustness after physical damage, adapting their architecture to the environment in real time.19PubMed Central. Biological solutions to transport network design
With both aspen groves and fungal networks, the colony-versus-individual question feels less like a semantic game and more like a genuine gap in how we classify living things. A fungal mycelium has no clear boundary between one “individual” and the surrounding network. A clonal aspen grove shares a genome but has stems that can die independently. The word “colony” papers over this ambiguity by describing the group without forcing a verdict on whether it is one thing or many.
Vertebrate Breeding Colonies
When applied to vertebrates, “colony” usually means something much looser: a breeding aggregation. Seabird colonies, bat roosts, and prairie dog towns bring together hundreds or thousands of individuals who share a location for reproduction but remain distinct, self-contained animals. No one would mistake a seabird colony for a superorganism. Yet the word is not just a label of convenience. Colonial breeding in birds comes with measurable costs and benefits that shape the colony’s size and location.
One hypothesis for why seabirds breed in colonies rather than dispersed nests is that coloniality concentrates foragers, leading to faster discovery of food patches through local enhancement: birds follow their departing or returning neighbors to feeding areas. Modeling work suggests that colonial breeding is favored when food patches are large or short-lived enough that competition among foragers is softened, while dispersed nesting wins out when patches are small or persistent.20University of Chicago Press / The American Naturalist. Spatial-concentration effects and the importance of local enhancement in the evolution of colonial breeding in seabirds
The costs are equally real. In colonial kittiwake populations, fledgling body condition drops as breeding density increases within the immediate nesting area and within the broader foraging range, probably because of density-dependent food depletion.21PubMed Central. Offspring body condition and immunocompetence are negatively affected by high breeding densities in a colonial seabird: a multiscale approach Larger colonies also attract more parasites: transient birds visiting bigger cliff swallow colonies are more likely to introduce parasites, contributing to a positive relationship between colony size and parasite load.22Ecology. Empirical measurement of parasite transmission between groups in a colonial bird The vertebrate colony, then, is a trade-off structure: grouping brings information benefits and predator dilution, but it also intensifies competition and disease risk.
Eusocial Mammals
Most vertebrate colonies lack the rigid division of labor seen in insect societies, but naked mole-rats are a dramatic exception. These subterranean rodents live in groups of up to roughly 300 individuals with a single breeding female and a handful of breeding males. Around 99 percent of individuals may never reach reproductive maturity, instead spending their lives foraging and maintaining the tunnel system.23PubMed Central. The relationship between individual phenotype and the division of labour in naked mole-rats: it’s complicated The parallels with insect eusociality are striking: extreme reproductive skew, overlapping generations living together, and cooperative care of the queen’s offspring. Naked mole-rat colonies are arguably the closest mammalian analogue to an ant colony, though the mechanisms that enforce reproductive suppression involve hormonal signals rather than the genetic switches seen in hymenopteran insects.
How Colonies Recognize Their Own Members
For a colony to function, its members typically need a way to distinguish insiders from outsiders. In social insects, this often relies on cuticular hydrocarbons: chemical signatures on the body surface that nestmates learn to recognize. Kin selection theory predicts that cooperation evolves most readily among relatives, and phylogenetic analyses confirm that eusociality in ants, bees, and wasps evolved in groups with high within-colony relatedness, typically mother-offspring groups.24Current Biology. Kin selection and altruism
Colonial marine invertebrates use a different toolkit. In botryllid ascidians (sea squirts that grow as colonies of interconnected zooids), two types of recognition govern colony boundaries. A single highly polymorphic gene locus controls whether two colonies fuse or reject each other: colonies sharing at least one allele at this locus fuse into a chimera, while colonies with no shared alleles reject each other.25PubMed. Allorecognition in compound ascidians This sounds like a system designed to promote fusion with relatives, and for years that was the standard interpretation. But chimeric colonies turn out to be unstable, with one genotype often outcompeting the other over time. That instability has led some researchers to argue that the real selective pressure driving allorecognition is fusion with self rather than fusion with kin: the system primarily prevents parasitism by unrelated genotypes rather than facilitating altruistic cooperation with relatives.26PubMed. Allorecognition in Colonial Marine Invertebrates: Does Selection Favor Fusion with Kin of Fusion with Self?
This distinction matters for how we think about colonies more generally. If recognition systems are mostly about keeping outsiders out rather than actively embracing kin, then the colony boundary is as much a defensive border as a cooperative scaffold.
When a Colony Becomes an Organism
The deepest question lurking behind every use of “colony” is where group living tips over into genuine multicellularity. The volvocine algae, a family of green algae, offer a living gradient. At one end of the spectrum are single-celled species. In the middle are colonial forms: clusters of cells that stick together after division but remain functionally interchangeable. At the other end sits Volvox, which has a full division of labor between small somatic cells and large reproductive cells.27PubMed Central. Origins of multicellular complexity: Volvox and the volvocine algae This spectrum, from unicellular to colonial to fully multicellular with germ-soma specialization, makes volvocine algae a model system for studying how the transition to multicellularity occurs.28PubMed Central. Evolution of reproductive development in the volvocine algae
Research on Volvox carteri suggests that fitness trade-offs drive the transition. As cell groups increase in size, the cost of reproduction for any individual cell grows, creating selective pressure for some cells to specialize in vegetative functions and give up reproduction altogether. This reproductive altruism, analogous to the sterile worker caste in insect colonies, transforms a colonial cluster into something that looks more like a single organism with differentiated tissues.29PubMed Central. Evolution of individuality during the transition from unicellular to multicellular life The genetic basis for this shift may have originated through the cooption of a gene that already existed in a unicellular ancestor, where it governed a life-history trade-off rather than a multicellular division of labor.30PubMed Central. Evolution of individuality during the transition from unicellular to multicellular life
Even environmental cues from other species can trigger the colonial transition. Choanoflagellates, the closest living relatives of animals, form multicellular rosettes in response to lipids produced by specific bacteria. Three structurally different classes of bacterial lipids have been found to activate, enhance, or inhibit rosette formation in the choanoflagellate Salpingoeca rosetta.31PubMed Central. Bacterial lipids activate, synergize, and inhibit a developmental switch in choanoflagellates A colony, in this case, is not an inevitable outcome of the organism’s genetics; it is a conditional response to the chemical landscape created by neighboring microbes.
Engineering Colonies From Scratch
Synthetic biologists have begun building artificial colonies by programming bacteria with gene circuits that produce coordinated spatial patterns. These engineered systems classify patterns into levels of increasing complexity, from arrangements with no diffusible signals to those with multiple interacting chemical gradients. The goal is not just to mimic nature but to create living materials with designed properties: biosensors that form visible patterns in response to environmental contaminants, or therapeutic biofilms that deliver drugs in controlled spatial configurations. The fact that researchers can recreate aspects of colonial behavior from a handful of genetic components suggests that coloniality, at its root, requires surprisingly little machinery. A few signal molecules, some response circuits, and physical proximity can get you a long way toward group-level coordination.
Conversely, breaking colonial behavior apart is also useful. Understanding how biofilm colonies resist antibiotics has become a priority in infectious disease research, because the strategies that work against free-floating bacteria often fail against the same species embedded in a matrix. Medical device design increasingly focuses on surface coatings and materials that prevent bacterial colonies from forming in the first place, rather than trying to kill established biofilms after the fact. The colony, here, is less a philosophical curiosity and more an engineering problem with direct consequences for patient outcomes.