Ants are eusocial insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants appear in the fossil record across the globe in considerable diversity during the latest Early Cretaceous and early Late Cretaceous, suggesting an earlier origin. Ants evolved from vespoid wasp ancestors in the Cretaceous period, and diversified after the rise of flowering plants. More than 13,800 of an estimated total of 22,000 species have been classified. They are easily identified by their geniculate (elbowed) antennae and the distinctive node-like structure that forms their slender waists.

Ants form colonies that range in size from a few dozen predatory individuals living in small natural cavities to highly organised colonies that may occupy large territories and consist of millions of individuals. Larger colonies consist of various castes of sterile, wingless females, most of which are workers (ergates), as well as soldiers (dinergates) and other specialised groups. Nearly all ant colonies also have some fertile males called "drones" and one or more fertile females called "queens" (gynes). The colonies are described as superorganisms because the ants appear to operate as a unified entity, collectively working together to support the colony.

Ants gathering food

Ants have colonised almost every landmass on Earth. The only places lacking indigenous ants are Antarctica and a few remote or inhospitable islands. Ants thrive in most ecosystems and may form 15–25% of the terrestrial animal biomass. Their success in so many environments has been attributed to their social organisation and their ability to modify habitats, tap resources, and defend themselves. Their long co-evolution with other species has led to mimetic, commensal, parasitic, and mutualistic relationships.

Ant societies have division of labour, communication between individuals, and an ability to solve complex problems. These parallels with human societies have long been an inspiration and subject of study. Many human cultures make use of ants in cuisine, medication, and rituals. Some species are valued in their role as biological pest control agents. Their ability to exploit resources may bring ants into conflict with humans, however, as they can damage crops and invade buildings. Some species, such as the red imported fire ant (Solenopsis invicta), are regarded as invasive species, establishing themselves in areas where they have been introduced accidentally.

The family Formicidae belongs to the order Hymenoptera, which also includes sawflies, bees, and wasps. Ants evolved from a lineage within the stinging wasps, and a 2013 study suggests that they are a sister group of the Apoidea.[11] In 1966, E. O. Wilson and his colleagues identified the fossil remains of an ant (Sphecomyrma) that lived in the Cretaceous period. The specimen, trapped in amber dating back to around 92 million years ago, has features found in some wasps, but not found in modern ants.[12] Sphecomyrma was possibly a ground forager, while Haidomyrmex and Haidomyrmodes, related genera in subfamily Sphecomyrminae, are reconstructed as active arboreal predators.[13] Older ants in the genus Sphecomyrmodes have been found in 99 million year-old amber from Myanmar.[14][15] A 2006 study suggested that ants arose tens of millions of years earlier than previously thought, up to 168 million years ago.[1] After the rise of flowering plants about 100 million years ago they diversified and assumed ecological dominance around 60 million years ago.[16][1][17][18] Some groups, such as the Leptanillinae and Martialinae, are suggested to have diversified from early primitive ants that were likely to have been predators underneath the surface of the soil.[3][19]

Ants fossilised in Baltic amber

During the Cretaceous period, a few species of primitive ants ranged widely on the Laurasian supercontinent (the Northern Hemisphere). They were scarce in comparison to the populations of other insects, representing only about 1% of the entire insect population. Ants became dominant after adaptive radiation at the beginning of the Paleogene period. By the Oligocene and Miocene, ants had come to represent 20–40% of all insects found in major fossil deposits. Of the species that lived in the Eocene epoch, around one in 10 genera survive to the present. Genera surviving today comprise 56% of the genera in Baltic amber fossils (early Oligocene), and 92% of the genera in Dominican amber fossils (apparently early Miocene).[16][20]

Termites live in colonies and are sometimes called ‘white ants’, but termites are not ants. They are the sub-order Isoptera, and together with cockroaches they form the order Blattodea. Blattodeans are related to mantids, crickets, and other winged insects that do not undergo full metamorphosis. Like ants, termites are eusocial, with sterile workers, but they differ greatly in the genetics of reproduction. The similarity of their social structure to that of ants is attributed to convergent evolution.[21] Velvet ants look like large ants, but are wingless female wasps.[22][23]

Friendship is a relationship of mutual affection between people.[1] It is a stronger form of interpersonal bond than an association, and has been studied in academic fields such as communication, sociology, social psychology, anthropology, and philosophy. Various academic theories of friendship have been proposed, including social exchange theory, equity theory, relational dialectics, and attachment styles.

Although there are many forms of friendship, some of which may vary from place to place, certain characteristics are present in many types of such bonds. Such characteristics include affection, kindness, love, virtue, sympathy, empathy, honesty, altruism, loyalty, generosity, forgiveness, mutual understanding and compassion, enjoyment of each other's company, trust, and the ability to be oneself, express one's feelings to others, and make mistakes without fear of judgment from the friend. Friendship is an essential aspect of relationship building skills.

Childhood

The understanding of friendship in children tends to be more heavily focused on areas such as common activities, physical proximity, and shared expectations.[2]:498[a] These friendships provide opportunity for playing and practicing self-regulation.[3]:246 Most children tend to describe friendship in terms of things like sharing, and children are more likely to share with someone they consider to be a friend.[3]:246[4][5] As children mature, they become less individualized and are more aware of others. They gain the ability to empathize with their friends, and enjoy playing in groups. They also experience peer rejection as they move through the middle childhood years. Establishing good friendships at a young age helps a child to be better acclimated in society later on in their life.[4]

Based upon the reports of teachers and mothers, 75% of preschool children had at least one friend. This figure rose to 78% through the fifth grade, as measured by co-nomination as friends, and 55% had a mutual best friend.[3]:247 About 15% of children were found to be chronically friendless, reporting periods without mutual friends at least six months.[3]:250

Potential benefits of friendship include the opportunity to learn about empathy and problem solving.[6] Coaching from parents can be useful in helping children to make friends. Eileen Kennedy-Moore describes three key ingredients of children's friendship formation: (1) openness, (2) similarity, and (3) shared fun.[7][8][9] Parents can also help children understand social guidelines they haven't learned on their own.[10] Drawing from research by Robert Selman[11] and others, Kennedy-Moore outlines developmental stages in children's friendship, reflecting an increasing capacity to understand others' perspectives: "I Want It My Way", "What's In It For Me?", "By the Rules", "Caring and Sharing", and "Friends Through Thick and Thin."[12]

Adolescence

Two friends in Bhutan

In adolescence, friendships become "more giving, sharing, frank, supportive, and spontaneous." Adolescents tend to seek out peers who can provide such qualities in a reciprocal relationship, and to avoid peers whose problematic behavior suggest they may not be able to satisfy these needs.[13] Personal characteristics and dispositions are also features sought by adolescents, when choosing whom to begin a friendship with.[14] Relationships begin to maintain a focus on shared values, loyalty, and common interests, rather than physical concerns like proximity and access to play things that more characterize childhood.[3]:246

A study performed at the University of Texas at Austin examined over 9,000 American adolescents to determine how their engagement in problematic behavior (such as stealing, fighting, and truancy) was related to their friendships. Findings indicated that adolescents were less likely to engage in problem behavior when their friends did well in school, participated in school activities, avoided drinking, and had good mental health. The opposite was found regarding adolescents who did engage in problematic behavior. Whether adolescents were influenced by their friends to engage in problem behavior depended on how much they were exposed to those friends, and whether they and their friendship groups "fit in" at school.[15]

A study by researchers from Purdue University found that friendships formed during post-secondary education last longer than friendships formed earlier.[16] In late adolescence cross-racial friendships tend to be uncommon, likely due to prejudice and cultural differences.[14]

Adulthood

Friendships in adulthood

Freundschaft zwischen Jonathan und David by Julius Schnorr von Karolsfeld (1860), which translates in English as Friendship between Jonathan and David

Two friends before posing for a picture.

Friendship in adulthood provides companionship, affection, as well as emotional support, and contributes positively to mental well-being and improved physical health.[17]:426

Adults may find it particularly difficult to maintain meaningful friendships in the workplace. "The workplace can crackle with competition, so people learn to hide vulnerabilities and quirks from colleagues. Work friendships often take on a transactional feel; it is difficult to say where networking ends and real friendship begins."[18] Most adults value the financial security of their jobs more than friendship with coworkers.[19]

The majority of adults have an average of two close friends.[20] Numerous studies with adults suggest that friendships and other supportive relationships do enhance self-esteem.[21]

Older adults

Older adults continue to report high levels of personal satisfaction in their friendships as they age, even as the overall number of friends tends to decline. This satisfaction is associated with an increased ability to accomplish activities of daily living, as well as a reduced decline in cognitive abilities, decreased instances of hospitalization, and better outcomes related to rehabilitation.[17]:427 The overall number of reported friends in later life may be mediated by increased lucidity, better speech and vision, and marital status.[22]:53

As one review phrased it:

Research within the past four decades has now consistently found that older adults reporting the highest levels of happiness and general well being also report strong, close ties to numerous friends.[23]

As family responsibilities and vocational pressures lessen, friendships become more important. Among the elderly, friendships can provide links to the larger community, serve as a protective factor against depression and loneliness, and compensate for potential losses in social support previously given by family members.[24]:32–33 Especially for people who cannot go out as often, interactions with friends allow for continued societal interaction. Additionally, older adults in declining health who remain in contact with friends show improved psychological well-being.[25]

Spiders (order Araneae) are air-breathing arthropods that have eight legs, chelicerae with fangs generally able to inject venom,[2] and spinnerets that extrude silk.[3] They are the largest order of arachnids and rank seventh in total species diversity among all orders of organisms.[4] Spiders are found worldwide on every continent except for Antarctica, and have become established in nearly every habitat with the exceptions of air and sea colonization. As of July 2019, at least 48,200 spider species, and 120 families have been recorded by taxonomists.[1] However, there has been dissension within the scientific community as to how all these families should be classified, as evidenced by the over 20 different classifications that have been proposed since 1900.[5]

Anatomically, spiders (as with all arachnids) differ from other arthropods in that the usual body segments are fused into two tagmata, the prosoma, or cephalothorax, and opisthosoma, or abdomen, and joined by a small, cylindrical pedicel (however, as there is currently neither paleontological nor embryological evidence that spiders ever had a separate thorax-like division, there exists an argument against the validity of the term cephalothorax, which means fused cephalon (head) and the thorax. Similarly, arguments can be formed against use of the term abdomen, as the opisthosoma of all spiders contains a heart and respiratory organs, organs atypical of an abdomen[6]). Unlike insects, spiders do not have antennae. In all except the most primitive group, the Mesothelae, spiders have the most centralized nervous systems of all arthropods, as all their ganglia are fused into one mass in the cephalothorax. Unlike most arthropods, spiders have no extensor muscles in their limbs and instead extend them by hydraulic pressure.

Their abdomens bear appendages that have been modified into spinnerets that extrude silk from up to six types of glands. Spider webs vary widely in size, shape and the amount of sticky thread used. It now appears that the spiral orb web may be one of the earliest forms, and spiders that produce tangled cobwebs are more abundant and diverse than orb-web spiders. Spider-like arachnids with silk-producing spigots appeared in the Devonian period about 386 million years ago, but these animals apparently lacked spinnerets. True spiders have been found in Carboniferous rocks from 318 to 299 million years ago, and are very similar to the most primitive surviving suborder, the Mesothelae. The main groups of modern spiders, Mygalomorphae and Araneomorphae, first appeared in the Triassic period, before 200 million years ago.

The species Bagheera kiplingi was described as herbivorous in 2008,[7] but all other known species are predators, mostly preying on insects and on other spiders, although a few large species also take birds and lizards. It is estimated that the world's 25 million tons of spiders kill 400–800 million tons of prey per year.[8] Spiders use a wide range of strategies to capture prey: trapping it in sticky webs, lassoing it with sticky bolas, mimicking the prey to avoid detection, or running it down. Most detect prey mainly by sensing vibrations, but the active hunters have acute vision, and hunters of the genus Portia show signs of intelligence in their choice of tactics and ability to develop new ones. Spiders' guts are too narrow to take solids, so they liquefy their food by flooding it with digestive enzymes. They also grind food with the bases of their pedipalps, as arachnids do not have the mandibles that crustaceans and insects have.

To avoid being eaten by the females, which are typically much larger, male spiders identify themselves to potential mates by a variety of complex courtship rituals. Males of most species survive a few matings, limited mainly by their short life spans. Females weave silk egg-cases, each of which may contain hundreds of eggs. Females of many species care for their young, for example by carrying them around or by sharing food with them. A minority of species are social, building communal webs that may house anywhere from a few to 50,000 individuals. Social behavior ranges from precarious toleration, as in the widow spiders, to co-operative hunting and food-sharing. Although most spiders live for at most two years, tarantulas and other mygalomorph spiders can live up to 25 years in captivity.

While the venom of a few species is dangerous to humans, scientists are now researching the use of spider venom in medicine and as non-polluting pesticides. Spider silk provides a combination of lightness, strength and elasticity that is superior to that of synthetic materials, and spider silk genes have been inserted into mammals and plants to see if these can be used as silk factories. As a result of their wide range of behaviors, spiders have become common symbols in art and mythology symbolizing various combinations of patience, cruelty and creative powers. An irrational fear of spiders is called arachnophobia.