Many ants, bees, termites and wasps form societies in which members belong to social groups (castes) with different roles, such as reproduction or foraging.
The individual living things – organisms – in a colony often work together in such a coordinated way that they appear to be one entity, or ‘superorganism’.
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What is a superorganism?
A superorganism is a level of biological organisation above the organism. This concept was popularised by biologists Bert Hölldobler and EO Wilson in their 2009 book The Superorganism, but the two authors disagreed on an exact meaning of the word so there are several definitions. The clearest is in the book’s glossary: “A society that possesses features of organisation analogous to the physiological properties of single organisms.” Basically, a colony’s individuals are like parts of a body.
How is a colony like a body?
The key feature is division of labour. In a body, ‘germ’ cells such as sperm and egg are responsible for reproduction while ‘soma’ – body cells – do the other jobs. Similarly, in social insects, the reproductive caste handles genetic inheritance while the other castes, including workers and soldiers, carry out tasks such as finding food, caring for a young brood or protecting the nest.
A colony also has systems for specific purposes, like defence against disease. Just as the body’s immune system draws attention to parasites and can destroy an infected cell using molecules that punch holes in the cell’s membrane, an insect colony kills sick individuals. For example, Lasius neglectus (a relative of black garden ants) uses ‘destructive disinfection’: after detecting chemicals released by a pupa infected with parasitic fungi, worker ants will bite open the cuticle to spray antiseptic poison. This sacrifice prevents spread through the colony.
Can colonies be organisms?
Like body cells, individual insects collaborate as a cohesive unit. In fact, the superorganism concept was inspired by a 1911 essay by entomologist William Wheeler entitled ‘The ant-colony as an organism’. A colony has collective intelligence, too, because it’s structured like a brain: interactions among its members are akin to connections between neurones across a central nervous system, allowing features to arise that are more than the sum of its parts. These emergent properties, such as decision-making or the ability to map the outside world, aren’t directed by any one insect (or brain cell).
Why do social insects evolve?
Natural selection – survival of the fittest – favours organisms that promote their own survival and reproduction, their evolutionary ‘fitness’. But as Charles Darwin once said, “Selection may be applied to the family, as well as the individual.” This works as an individual who cooperates with close relatives (kin) promotes its ‘inclusive fitness’ by helping their shared genes to be inherited. This theory is called kin selection.
Are societies stable?
Not all social insects live in perfect harmony! In many ponerine ants, workers are ‘hopeful reproducers’ with a capacity to mate, driving competition among the genetically identical clones. No mating equals more cooperation, less conflict.
Stability is more likely in ‘eusocial’ (truly social) colonies with division of labour, overlapping generations and non-reproductive animals who care for young. For example, leaf-cutter ants use a complex caste system, based on size and age, and hundreds of thousands of sterile workers collect leaves to cultivate fungus farms to feed the colony. This utopian society is what creates a superorganism.
Are there other superorganisms?
One candidate is the Portuguese man o’ war. While it resembles a jellyfish, it’s actually a colony of individuals called zooids, which form parts of specialised structures such as stinging tentacles or the floating, gas-filled pneumatophore. Another example is Dictyostelium. These species of slime moulds normally live as single cells that hunt other amoebae but, during tough times, come together to build a multicellular body where a quarter of cells lose their reproductive ability and form a stalk to help spores disperse – a temporary superorganism.
Main image: A Portuguese man o' war/Getty
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