Sociality is the degree to which individuals in an animal population tend to associate in social groups (gregariousness) and form cooperative societies.

Sociality is a survival response to evolutionary pressures.[1] For example, when a mother wasp stays near her larvae in the nest, parasites are less likely to eat the larvae.[2] Biologists suspect that pressures from parasites and other predators selected this behavior in wasps of the family Vespidae.

This wasp behaviour evidences the most fundamental characteristic of animal sociality: parental investment. Parental investment is any expenditure of resources (time, energy, social capital) to benefit one's offspring. Parental investment detracts from a parent's capacity to invest in future reproduction and aid to kin (including other offspring). An animal that cares for its young but shows no other sociality traits is said to be subsocial.

An animal that exhibits a high degree of sociality is called a social animal. The highest degree of sociality recognized by sociobiologists is eusociality. A eusocial taxon is one that exhibits overlapping adult generations, reproductive division of labor, cooperative care of young, and—in the most refined cases—a biological caste system.

Solitary animals, such as the jaguar, do not associate except for courtship and mating. If an animal taxon shows a degree of sociality beyond courtship and mating, but lacks any of the characteristics of eusociality, it is said to be presocial.[3] Although presocial species are much more common than eusocial species, eusocial species have disproportionately large populations.[4]

Canis lupus pack surrounding Bison
Gray wolves hunting in a presocial pack encircle an American bison.


The entomologist Charles D. Michener published a classification system for presociality in 1969, building on the earlier work of Suzanne Batra (who coined the words eusocial and quasisocial in 1966).[5][6] Michener used these terms in his study of bees, but also saw a need for additional classifications: subsocial, communal, and semisocial. In his use of these words, he did not generalize beyond insects. E. O. Wilson later refined Batra's definition of quasisocial.[7]


Subsociality is common in the animal kingdom. In subsocial taxa, parents care for their young for some length of time. Even if the period of care is very short, the animal is still described as subsocial. If adult animals associate with other adults, they are not called subsocial, but are ranked in some other classification according to their social behaviours. If occasionally associating or nesting with other adults is a taxon's most social behaviour, then members of those populations are said to be solitary but social. See Wilson (1971)[8] for definitions and further sub-classes of varieties of subsociality. Choe & Crespi (1997)[9] and Costa (2006) [10] give readable overviews.

Insect groups with species exhibiting subsociality include:






Embioptera[16] [17].

Hemiptera[18][19]: many families, including Membracidae[20][21], Pentatomidae[22], Reduviidae[23][24][25], Tingidae[26]. Paternal care is known in some reduviids.[27]


Coleoptera [28]. Species and clades in multiple families: Erotylidae[29], Scarabaeidae[30] [31], Silvanidae,



Passalidae[34][35][36] The biology of Odontotaenius disjunctus (Illiger) is summarized by Bibbs et al.[37],

Silphidae[38], Staphylinidae[39][40]




Other Curculionidae.

Chrysomelidae. In the leaf beetles, subsociality has been documented in two subfamilies, Cassidinae and Chrysomelinae.[46][47][48]. In Cassidinae (43 tribes, 325 genera, ~6000 species), maternal guarding of broods (eggs, larvae, pupae) is documented so far in two tribes (in the derived tortoise beetles clade[49]). In the Neotropical tribe Eugenysini, it appears in both Agenysa and Eugenysa[50]. In the tribe Mesomphaliini, subsocial species are documented in Acromis[51], Omaspides, and Paraselenis. In Chrysomelinae (150 genera, ~3000 species), maternal guarding of eggs and larvae is known in three tribes: Doryphorini: Doryphora and Platyphora; Gonioctenini: Gonioctena; and Phyllocharitini: Pterodunga mirabile in Australia[52]. See Chaboo et al. 2014 for a molecular-based phylogeny of Chrysomelinae and discussion of the origin of maternal care. Generally, reproductive and defense strategies in this subfamily are very diverse, with situations of ovoviviparity and viviparity and chemical defense[53].



Solitary but social

Microcebus murinus -Artis Zoo, Amsterdam, Netherlands-8c
The mouse lemur is a nocturnal, solitary-but-social lemur native to Madagascar.

Solitary-but-social animals forage separately, but some individuals sleep in the same location or share nests. The home ranges of females usually overlap, whereas those of males do not. Males usually do not associate with other males, and male offspring are usually evicted upon maturity. Among primates, this form of social organization is most common among the nocturnal strepsirrhine species and tarsiers. Some examples of solitary-but-social species are mouse lemurs, lorises, and orangutans.[55]


Sociobiologists place communal, quasisocial, and semisocial animals into a meta-class: the parasocial. The two commonalities of parasocial taxa are the exhibition of parental investment, and socialization in a single, cooperative dwelling.[3]

Communal, quasisocial, and semisocial groups differ in a few ways. In a communal group, adults cohabit in a single nest site, but they each care for their own young. Quasisocial animals cohabit, but they also share the responsibilities of brood care. (This has been observed in some Hymenoptera and spider taxa,[56] as well as in some other invertebrates.)[3] A semisocial population has the features of communal and quasisocial populations, but they also have a biological caste system that delegates labor according to whether or not an individual is able to reproduce.

Beyond parasociality is eusociality. Eusocial insect societies have all the characteristics of a semisocial one, except overlapping generations of adults cohabit and share in the care of young. This means that more than one adult generation is alive at the same time, and that the older generations also care for the newest offspring.


Natural Beehive and Honeycombs
Giant honey bees cover the honeycomb of their nest.

Eusocial societies have overlapping adult generations, cooperative care of young, and division of reproductive labor. When organisms in a species are born with physical characteristics specific to a caste which never changes throughout their lives, this exemplifies the highest acknowledged degree of sociality. Eusociality has evolved in several orders of insects. Common examples of eusociality are from Hymenoptera (ants, bees, sawflies, and wasps) and Blattodea (infraorder Isoptera, termites), but some Coleoptera (such as the beetle Austroplatypus incompertus), Hemiptera (bugs such as Pemphigus spyrothecae), and Thysanoptera (thrips) are described as eusocial. Eusocial species that lack this criterion of morphological caste differentiation are said to be primitively eusocial.[3]

Two potential examples of primitively eusocial mammals are the naked mole-rat and the Damaraland mole-rat (Heterocephalus glaber & Fukomys damarensis, respectively).[57] Both species are diploid and highly inbred, and they aid in raising their siblings and relatives, all of whom are born from a single reproductive queen. They usually live in harsh or limiting environments. However, a study conducted by O’Riain and Faulkes in 2008 suggests that due to regular inbreeding avoidance, mole rats sometimes outbreed and establish new colonies when resources are sufficient.[58]

Eusociality has arisen among some crustaceans that live in groups in a restricted area. Synalpheus regalis are parasitic shrimp that rely on fortress defense. They live in groups of closely related individuals, amidst tropical reefs and sponges.[59] Each group has one breeding female; she is protected by a large number of male defenders who are armed with enlarged snapping claws. As with other eusocial societies, there is a single shared living space for the colony members, and the non-breeding members act to defend it.[60]

Human eusociality

E. O. Wilson and Bert Hölldobler controversially[61] claimed in 2005 that humans exhibit sufficient sociality to be counted as a eusocial species, and that this enabled them to enjoy spectacular ecological success and dominance over ecological competitors.[62]

Comparison of sociality classifications

Degree of sociality Parental investment Cohabitation of all
adults and young
Cooperative care
of young
Reproductive division of labour Caste system Overlapping adult generations
Subsocial Yes No No No No No
Solitary but social Yes Sometimes No No No No
Communal Yes Yes No No No No
Quasisocial Yes Yes Yes No No No
Semisocial Yes Yes Yes Yes Yes No
Eusocial Yes Yes Yes Yes Yes Yes


In social psychology and biology, researchers have found the presence of corporate group social organization amongst animal species.[63] Research has shown that penguins are known to reside in densely populated corporate breeding colonies.[63]

See also


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Anelosimus is a cosmopolitan genus of cobweb spiders (Theridiidae), currently containing 74 species. Anelosimus is a key group in the study of sociality and its evolution in spiders (Aviles 1997). It contains species spanning the spectrum from solitary to highly social (quasisocial), with eight quasisocial species, far more than any other spider genus. Among these is the South American social species Anelosimus eximius, among the best studied social spider species.

The web of a colony of A. eximius can reach cover entire tree canopies and contain tens of thousands of individuals. Most of the highly social species live in lowland tropical forests, and all occur in the Americas. Other species, particularly those at higher altitudes in northern latitudes in the Americas and all non-American species appear to be solitary or sub-social. Social Anelosimus species are generally highly inbred and have female-biased sex ratios, with up to 10 females per male.

The social, subsocial, and solitary behavior of differing species within Anelosimus has been used to examine hypotheses of environmental pressures on social behavior, and inbreeding. Subsociality as a trait seems to be conserved, despite the wide range of environments in which Anelosimus species live; all known solitary species within the genus belong to a single clade. Sociality, however, has independently arisen several times.

Anelosimus eximius

Anelosimus eximius is a species of social spider in the genus Anelosimus, native to the Lesser Antilles and the area from Panama to Argentina. Colonies can comprise several thousand individuals.Anelosimus eximius are classified as a social spider species because they engage in shared brood care and cooperate to capture prey within their web, which allows them to capture prey much larger than a single individual would be able to.Their webs do not capture a lot of prey, but the prey that are caught are significantly larger than most prey captured in the webs of other individual social or antisocial spider species. Thus, their techniques provide more nutrients than other social spider colonies may obtain. These techniques are most efficient in Anelosimus eximius colonies of about 1,000 individuals.The sociality of Anelosimus eximius aids in the increased fitness of the species. One potential cost of sociality in Anelosimus eximius is that they produce fewer egg sacs. However, each egg sac holds more individual offspring than most arachnid egg sacs would normally hold. Thus, the benefits seem to outweigh the costs.It is difficult to explain how sociality has evolved from a typically solitary animal. One trait that has facilitated this shift is the lack of discrimination against foreign offspring. It has also been questioned whether the alloparental behavior of Anelosimus eximius was an ancestral trait or if the species had to overcome discrimination in order to gain their trait of sociality. Through studies on social and sub-social species that observed reactions to foreign offspring, scientists discovered that the species did not need to overcome discrimination; both sub-social and social species of arachnids showed no discrimination towards foreign offspring.A. eximius is preyed upon by Zatypota parasitoid wasps, the larva of which feed on the spider's hemolymph and induce the spider to move away and spin an abnormal web, serving as a cocoon for the pupating insect to feed on the spider and emerge. The process is particularly noteworthy because the actions induced do not seem to be part of the spider's typical behaviour repertoire.

Danah boyd

danah boyd (styled lowercase, born November 24, 1977 as Danah Michele Mattas) is a technology and social media scholar. She is a Principal Researcher at Microsoft Research, the founder and president of Data & Society Research Institute, and a Visiting Professor at New York University.

Emotion in animals

The existence and nature of emotions in animals are believed to be correlated with those of humans and to have evolved from the same mechanisms. Charles Darwin was one of the first scientists to write about the subject, and his observational (and sometimes anecdotal) approach has since developed into a more robust, hypothesis-driven, scientific approach. Cognitive bias tests and learned helplessness models, have shown feelings of optimism and pessimism in a wide range of species including rats, dogs, cats, rhesus macaques, sheep, chicks, starlings, pigs, and honeybees.Some behaviourists, such as John B. Watson, claim that stimulus–response models provide a sufficient explanation for animal behaviours that have been described as emotional, and that all behaviour, no matter how complex, can be reduced to a simple stimulus-response association. Watson described that the purpose of psychology was "to predict, given the stimulus, what reaction will take place; or given the reaction, state what the situation or stimulus is that has caused the reaction".

Ernst Fehr

Ernst Fehr (born June 21, 1956 in Hard, Austria) is an Austrian-Swiss behavioral economist and neuroeconomist and a Professor of Microeconomics and Experimental Economic Research, as well as the vice chairman of the Department of Economics at the University of Zürich, Switzerland. His research covers the areas of the evolution of human cooperation and sociality, in particular fairness, reciprocity and bounded rationality.

He is also well known for his important contributions to the new field of neuroeconomics, as well as to behavioral economics, behavioral finance and experimental economics. According to IDEAS/REPEC, he is the second-most influential German-speaking economist, and is ranked at 86th globally.In 2010 Ernst Fehr founded, together with his brother, Gerhard Fehr, FehrAdvice & Partners, the first globally operating consultancy firm completely dedicated to behavioral economics.

In 2016, Fehr was ranked as the most influential economist in Germany, Austria, and Switzerland.


Eusociality (from Greek εὖ eu "good" and social), the highest level of organization of sociality, is defined by the following characteristics: cooperative brood care (including care of offspring from other individuals), overlapping generations within a colony of adults, and a division of labor into reproductive and non-reproductive groups. The division of labor creates specialized behavioral groups within an animal society which are sometimes called castes. Eusociality is distinguished from all other social systems because individuals of at least one caste usually lose the ability to perform at least one behavior characteristic of individuals in another caste.

Eusociality exists in certain insects, crustaceans and mammals. It is mostly observed and studied in the Hymenoptera (ants, bees, and wasps) and in termites. A colony has caste differences: Queens and reproductive males take the roles of the sole reproducers, while soldiers and workers work together to create a living situation favorable for the brood. In addition to Hymenoptera and Isoptera, there are two known eusocial vertebrates among rodents: the naked mole-rat and the Damaraland mole-rat. Some shrimps, such as Synalpheus regalis, are also eusocial. E. O. Wilson and others have claimed that humans have evolved a weak form of eusociality (e.g., with menopause), but these arguments have been disputed.

Evolution of morality

The evolution of morality refers to the emergence of human moral behavior over the course of human evolution. Morality can be defined as a system of ideas about right and wrong conduct. In everyday life, morality is typically associated with human behavior, and not much thought is given to the social conducts of other creatures. The emerging fields of evolutionary biology and in particular sociobiology have argued that, though human social behaviors are complex, the precursors of human morality can be traced to the behaviors of many other social animals. Sociobiological explanations of human behavior are still controversial. The traditional view of social scientists has been that morality is a construct, and is thus culturally relative, although others argue that there is a science of morality.

Face-to-face (philosophy)

The face-to-face relation (French: rapport de face à face) is a concept in the French philosopher Emmanuel Lévinas' thought on human sociality. It means that, ethically, people are responsible to one-another in the face-to-face encounter. Specifically, Lévinas says that the human face "orders and ordains" us. It calls the subject into “giving and serving” the Other.

Gray marmot

The gray marmot, grey marmot, or Altai marmot (Marmota baibacina) is a species of rodent in the squirrel family Sciuridae. It is one of the larger marmots in the genus Marmota. It occurs in mountainous grasslands and shrub lands of central Asia, and is one of the 9 Palearctic (Eurasia) species. It is found in Xinjiang Province in China, southeastern Kazakhstan, Kyrgyzstan, Mongolia, and in the Altai and Tien Shan Mountains in southeastern Siberia in Russia. In the Mongolian Altai, its range overlaps with that of the Tarbagan marmot. Gray marmots form social groups, live in burrows, and hibernate.


Within the insect order Hymenoptera, the Halictinae are the largest, most diverse, and most recently diverged of the four halictid subfamilies. They comprise over 2400 bee species belonging to the five taxonomic tribes Augochlorini, Thrinchostomini, Caenohalictini, Sphecodini, and Halictini, which some entomologists alternatively organize into the two tribes Augochlorini and Halictini.The subfamily Halictinae also belongs to the hymenopteran monophyletic clade Aculeata, whose members are characterized by the possession of a modified ovipositor in the form of a poisonous sting for predator and prey defense. Including all eusocial and cleptoparasitic Halictidae taxa, these small bees are pollen feeders who mass provision their young and exhibit a broad spectrum of behavioral social polymorphies, ranging from solitary nesting to obligate eusociality. Estimated from the fossil record, eusociality in this subfamily evolved about 20 to 22 million years ago, which is relatively recent in comparison with other inferred eusociality origins. Thus, the Halictinae are believed to model the primitive eusociality of advanced eusocial hymenopterans. Because of their polymorphic sociality and recently evolved eusociality, the Halictinae are valuable to the study of social evolution.

Homo ergaster

Homo ergaster , also Homo erectus ergaster or African Homo erectus is an extinct chronospecies of the genus Homo that lived in eastern and southern Africa during the early Pleistocene, between about 1.9 million and 1.4 million years ago.

Originally proposed as a separate species, H. ergaster is now mostly considered either an early form, or an African variety, of H. erectus.The binomial name was published in 1975 by Groves and Mazák. The specific epithet, "ergaster", is derived from the Ancient Greek ἐργαστήρ ergastḗr - "workman", in reference to the advanced lithic technology developed by the species, thereby introducing the Acheulean industry.

KNM-ER 2598, a "H. erectus-like" occipital bone stands as the earliest evidence for H. erectus in Africa at approximately 1.9 million years ago (contemporary with Homo rudolfensis).

There is a fossil gap between 1.9 and 1.6 million years ago, KNM-ER 3733 is the oldest known H. ergaster skull dated to about 1.6 million years ago.

Its survival past 1.4 million years ago is uncertain, again due to a fossil gap, the next available African fossils allowing reliable morphological analysis are those of Homo rhodesiensis (African H. heidelbergensis), at 0.6 million years ago.


The sweat bee genus Lasioglossum is the largest of all bee genera, containing over 1700 species in numerous subgenera worldwide. They are highly variable in size, coloration, and sculpture; among the more unusual variants, some are cleptoparasites, some are nocturnal, and some are oligolectic. Most Lasioglossum species nest in the ground, but some nest in rotten logs.

The genus Lasioglossum can be divided into two informal series based on the strength of the distal veins of the forewing. The Lasioglossum series (or strong-veined Lasioglossum) is mostly composed of solitary or communal species. Two possible exceptions are L. aegyptiellum and L. rubricaudis, both of which show signs of division of labour indicative of eusociality.

The Hemihalictus series (or weak-veined Lasioglossum) includes species with a wide range of sociality. The Hemihalictus series is composed of species which are solitary, communal, semisocial, primitively eusocial, cleptoparasitic, or socially parasitic. Eusocial species may have small colonies with only one or a few workers or large colonies with dozens of workers. The largest colony sizes occur in L. marginatum, which forms perennial colonies lasting five or six years, with hundreds of workers.

Pack hunter

A pack hunter or social predator is a predatory animal which hunts its prey by working together with other members of its species. Normally animals hunting in this way are closely related, and with the exceptions of chimpanzees where only males normally hunt, all individuals in a family group contribute to hunting. When hunting cooperation is across two or more species, the broader term cooperative hunting is commonly used.

A well known pack hunter is the gray wolf; humans too can be considered pack hunters. Other pack hunting mammals include chimpanzees, dolphins, lions, dwarf and banded mongooses and spotted hyenas. Avian social predators include the Harris's hawk, butcherbirds, three of four kookaburra species and many helmetshrikes. There are a few cold-blooded pack hunters including simple arthropods such as army ants, the goldsaddle goatfish and occasionally crocodiles.Some non-avian theropod dinosaurs may have displayed pack behaviour.Pack hunting is typically associated with cooperative breeding and its concentration in the Afrotropical Region is a reflection of this. Most pack hunters are found in the southern African savannas, with a notable absence in tropical rainforests and with the exception of the wolf and coyote, higher latitudes. It is thought that either on the ancient and poor soils of the southern African savanna it is not possible for individual predators to find adequate food, or that the environment’s inherent unpredictability due to ENSO or IOD events means that in very bad conditions it will not be possible to raise the young necessary to prevent declining populations from adult mortality. It is also argued that Africa's large area of continuous flat and open country, which was even more extensive while rainforest contracted during glacial periods of the Quaternary, may have helped encourage pack hunting to become much more common than on any other continent.A shared pack hunting history is thought to be the main conduit through which humans formed a mutual relationship with dogs (that is, domestication), as both species are highly social and inter-dependent. Humans easily take over the dominance hierarchy of dogs as subordinates instinctively follow the “alpha” individual and dogs are accustomed to living very close together80-95% of carnivores are solitary and hunt alone; the others including lions, wild dogs, spotted hyenas, chimpanzees, and humans hunt cooperatively, at least some of the time. Cooperative hunting has also been documented in birds of prey and large marine vertebrates such as groupers and moray eels. Cooperative hunting has been linked to the social organization of animal species and the evolution of sociality and thus provides a unique perspective to study group behavior.

Primate sociality

Primate sociality is an area of primatology that aims to study the interactions between three main elements of a primate social network: the social organisation, the social structure and the mating system. The intersection of these three structures describe the socially complex behaviours and relationships occurring among adult males and females of a particular species. Cohesion and stability of groups are maintained through a confluence of factors, including: kinship, willingness to cooperate, frequency of agonistic behaviours, or varying intensities of dominance structures.Primate social organisation exists along a spectrum, with networks ranging from the solitary neighbourhood systems to the multi-individual units to the complex multilevel societies that are composed of hierarchically-organised social units. The evolution of diverse primate social systems is considered to be a naturally selected anti-predation response. Increased resource detection, cooperation and social learning are also considered as co-benefits of group living.


A prokaryote is a unicellular organism that lacks a membrane-bound nucleus, mitochondria, or any other membrane-bound organelle. The word prokaryote comes from the Greek πρό (pro) "before" and κάρυον (karyon) "nut or kernel". Prokaryotes are divided into two domains, Archaea and Bacteria. Species with nuclei and organelles are placed in the third domain, Eukaryota. Prokaryotes reproduce without fusion of gametes. The first living organisms are thought to have been prokaryotes.

In the prokaryotes, all the intracellular water-soluble components (proteins, DNA and metabolites) are located together in the cytoplasm enclosed by the cell membrane, rather than in separate cellular compartments. Bacteria, however, do possess protein-based bacterial microcompartments, which are thought to act as primitive organelles enclosed in protein shells. Some prokaryotes, such as cyanobacteria, may form large colonies. Others, such as myxobacteria, have multicellular stages in their life cycles.Molecular studies have provided insight into the evolution and interrelationships of the three domains of biological species. Eukaryotes are organisms, including humans, whose cells have a well defined membrane-bound nucleus (containing chromosomal DNA) and organelles. The division between prokaryotes and eukaryotes reflects the existence of two very different levels of cellular organization. Distinctive types of prokaryotes include extremophiles and methanogens; these are common in some extreme environments.

Schmidt sting pain index

The Schmidt sting pain index is a pain scale rating the relative pain caused by different hymenopteran stings. It is mainly the work of Justin O. Schmidt (born 1947), an entomologist at the Carl Hayden Bee Research Center in Arizona. Schmidt has published a number of papers on the subject, and claims to have been stung by the majority of stinging Hymenoptera.

His original paper in 1983 was a way to systematize and compare the hemolytic properties of insect venoms. The index contained in the paper started from 0 for stings that are completely ineffective against humans, progressed through 2, a familiar pain such as a common bee or wasp sting and finished at 4 for the most painful stings. Synoeca septentrionalis, along with other wasps in the genus Synoeca, bullet ants and tarantula hawks were the only species to attain this ranking. In the conclusion, some descriptions of the most painful examples were given, e.g.: "Paraponera clavata stings induced immediate, excruciating pain and numbness to pencil-point pressure, as well as trembling in the form of a totally uncontrollable urge to shake the affected part."

Subsequently, Schmidt has refined his scale, culminating in a paper published in 1990, which classifies the stings of 78 species and 41 genera of Hymenoptera. Schmidt described some of the experiences in vivid detail.An entry in The Straight Dope reported that "implausibly exact numbers" which do not appear in any of Schmidt’s published scientific papers were "wheedled out of him" by Outside magazine for an article it published in 1996.In September 2015, Schmidt was co-awarded the Ig Nobel Physiology and Entomology prize with Michael Smith, for their Hymenoptera research.

Social spider

A social spider is a spider species whose individuals form relatively long-lasting aggregations. Whereas most spiders are solitary and even aggressive toward other members of their own species, some hundreds of species in several families show a tendency to live in groups, often referred to as colonies.


Theridiidae is a large family of spiders, also known as the tangle-web spiders, cobweb spiders and comb-footed spiders. Members of Theridiidae are the most common arthropods found in human dwellings throughout the world. The diverse, globally distributed family includes over 2,200 species in over 100 genera of three-dimensional space-web-builders. Theridiid spiders are entelegyne (have a genital plate in the female) araneomorph ecribellate (use sticky capture silk instead of woolly silk) spiders that often build tangle space webs and have a comb of serrated bristles (setae) on the tarsus of the fourth leg.

The family includes some model organisms for research, for example, the genus Latrodectus, the medically important widow spiders. In addition to studies characterizing their venom and its clinical manifestation, widow spiders are broadly used in research on spider silk, and on sexual biology including sexual cannibalism.

Anelosimus spiders are also model organisms, used for the study of sociality, its evolution, and its ecological and evolutionary causes and consequences. They are particularly important for such studies as the genus contains species varying from solitary to permanently social, and because sociality has evolved frequently within the genus allowing comparative studies across species. These spiders are also a promising model for the study of inbreeding as their mating system co-varies with sociality, and all permanently social species are highly inbred.

One species in Theridion, the Hawaiian T. grallator, is used as a model to understand the selective forces and the genetic basis of colour polymorphism within species. Theridion grallator is known as the "happyface" spider, as certain morphs have a pattern uncannily resembling a smiley face or a grinning clown face on their yellow body.

The family also contains the well studied kleptoparasitic species of the subfamily Argyrodinae (including Argyrodes, Faiditus, and Neospintharus) which often have triangular bodies. These spiders live in the webs of larger spiders and pilfer small prey caught by their host's web, eat prey killed by the host spider, and may consume silk from the host web, as well as attack and eat the host itself.

The largest genus with over 600 species currently placed in it is Theridion, but it is not monophyletic. Another large genus is Parasteatoda, previously Achaearanea, which includes the North American common house spider.

Many theridiids trap ants and other ground dwelling insects by means of elastic sticky silk trap lines leading to the soil surface. Despite their name, cobweb or tangle-web spiders have a huge range of web architectures.

Western Palaearctic

The Western Palaearctic or Western Palearctic is part of the Palaearctic ecozone, one of the eight ecozones dividing the Earth's surface. Because of its size, the Palaearctic is often divided for convenience into two, with Europe, North Africa, northern and central parts of the Arabian Peninsula, and part of temperate Asia, roughly to the Ural Mountains forming the western zone, and the rest of temperate Asia becoming the Eastern Palaearctic. Its exact boundaries differ depending on the authority in question, but the Handbook of the Birds of Europe, the Middle East, and North Africa: The Birds of the Western Palearctic) (BWP) definition is widely used, and is followed by the most popular Western Palearctic checklist, that of the Association of European Rarities Committees (AERC). The Western Palearctic ecozone includes mostly boreal and temperate climate ecoregions.The Palaearctic region has been recognised as a natural zoogeographic region since Sclater proposed it in 1858. The oceans to the north and west, and the Sahara to the south are obvious natural boundaries with other ecozones, but the eastern boundary is more arbitrary, since it merges into another part of the same ecozone, and the mountain ranges used as markers are less effective biogeographic separators. The climate differences across the Western Palearctic region can cause behavioral differences within the same species across geographical distance, such as in the sociality of behavior for bees of the species Lasioglossum malachurum.


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