Tarantism is a form of hysteric behaviour, popularly believed to result from the bite of the wolf spider "Lycosa tarantula" (distinct from the broad class of spiders also called tarantulas).

A better candidate cause is "Latrodectus tredecimguttatus", commonly known as the Mediterranean black widow or steppe spider, although no link between such bites and the behaviour of tarantism has ever been demonstrated. However, the term historically is used to refer to a dancing mania - characteristic of southern Italy - which likely had little to do with spider bites. The tarantella dance supposedly evolved from this therapy.

Mass psychogenic illness (MPI), also called mass sociogenic illness or just sociogenic illness, is "the rapid spread of illness signs and symptoms affecting members of a cohesive group, originating from a nervous system disturbance involving excitation, loss, or alteration of function, whereby physical complaints that are exhibited unconsciously have no corresponding organic" cause. MPI is distinct from other collective delusions, also included under the blanket terms of mass hysteria, in that MPI causes symptoms of disease, though there is no organic cause.

There is a clear preponderance of female victims. The DSM-IV-TR does not have specific diagnosis for this condition but the text describing conversion disorder states that "In 'epidemic hysteria', shared symptoms develop in a circumscribed group of people following 'exposure' to a common precipitant."

Dancing mania (also known as dancing plague, choreomania, St John's Dance and, historically, St. Vitus's Dance) was a social phenomenon that occurred primarily in mainland Europe between the 14th and 17th centuries. It involved groups of people dancing erratically, sometimes thousands at a time. The mania affected men, women, and children who danced until they collapsed from exhaustion. One of the first major outbreaks was in Aachen, in the Holy Roman Empire, in 1374, and it quickly spread throughout Europe; one particularly notable outbreak occurred in Strasbourg in 1518, also in the Holy Roman Empire.

Affecting thousands of people across several centuries, dancing mania was not an isolated event, and was well documented in contemporary reports. It was nevertheless poorly understood, and remedies were based on guesswork. Generally, musicians accompanied dancers, to help ward off the mania, but this tactic sometimes backfired by encouraging more to join in. There is no consensus among modern-day scholars as to the cause of dancing mania.

The several theories proposed range from religious cults being behind the processions to people dancing to relieve themselves of stress and put the poverty of the period out of their minds. It is, however, thought to have been a mass psychogenic illness in which the occurrence of similar physical symptoms, with no known physical cause, affect a large or small group of people as a form of social influence.

Qualities of MPI outbreaks often include:

- symptoms that have no plausible organic basis;

- symptoms that are transient and benign;

- symptoms with rapid onset and recovery;

- occurrence in a segregated group;

- the presence of extraordinary anxiety;

- symptoms that are spread via sight, sound or oral communication;

- a spread that moves down the age scale, beginning with older or higher-status people;

- a preponderance of female participants

Also, the illness may recur after the initial outbreak.

The outbreaks of dancing mania varied, and several characteristics of it have been recorded. Generally occurring in times of hardship, up to tens of thousands of people would appear to dance for hours, days, weeks, and even months.

Women have often been portrayed in modern literature as the usual participants in dancing mania, although contemporary sources suggest otherwise. Whether the dancing was spontaneous, or an organised event, is also debated. What is certain, however, is that dancers seemed to be in a state of unconsciousness, and unable to control themselves.

In his research into social phenomena, author Robert Bartholomew notes that contemporary sources record that participants often did not reside where the dancing took place. Such people would travel from place to place, and others would join them along the way. With them they brought customs and behaviour that were strange to the local people. Bartholomew describes how dancers wore "strange, colorful attire" and "held wooden sticks".

Robert Marks, in his study of hypnotism, notes that some decorated their hair with garlands. However, not all outbreaks involved foreigners, and not all were particularly calm. Bartholomew notes that some "paraded around naked" and made "obscene gestures". Some even had sexual intercourse. Others acted like animals, and jumped, hopped and leaped about.

They hardly stopped, and some danced until they broke their ribs and subsequently died. Throughout, dancers screamed, laughed, or cried, and some sang. Bartholomew also notes that observers of dancing mania were sometimes treated violently if they refused to join in. Participants demonstrated odd reactions to the colour red; in "A History of Madness in Sixteenth-Century Germany", Midelfort notes they "could not perceive the color red at all", and Bartholomew reports "it was said that dancers could not stand... the color red, often becoming violent on seeing [it]".

Bartholomew also notes that dancers "could not stand pointed shoes", and that dancers enjoyed their feet being hit. Throughout, those affected by dancing mania suffered from a variety of ailments, including chest pains, convulsions, hallucinations, hyperventilation, epileptic fits, and visions. In the end, most simply dropped down, overwhelmed with exhaustion. Midelfort, however, describes how some ended up in a state of ecstasy. Typically, the mania was contagious but it often struck small groups, such as families and individuals.

John Crompton proposed that ancient Bacchanalian rites that had been suppressed by the Roman Senate in 186 BC went underground, reappearing under the guise of emergency therapy for bite victims.

The phenomenon of tarantism is consistent with mass psychogenic illness.

Although the popular belief persists that tarantism results from a spider bite, it remains scientifically unsubstantiated. Donaldson, Cavanagh, and Rankin (1997) conclude that the actual cause or causes of tarantism remain unknown.

Almost all spiders are venomous, but not all spider bites result in the injection of venom. Pain from non-venomous, so-called "dry bites" typically lasts for 5 to 60 minutes while pain from envenomating spider bites may last for longer than 24 hours. Bleeding also may occur with a bite. Signs of a bacterial infection due to a spider bite occur infrequently (0.9%).

A study of 750 definite spider bites in Australia indicated that 6% of spider bites cause significant effects, the vast majority of these being redback spider bites causing significant pain lasting more than 24 hours. Activation of the sympathetic nervous system can lead to sweating, high blood pressure and gooseflesh.

Most recluse spider bites are minor with little or no necrosis. However, a small number of bites produce necrotic skin lesions. First pain and tenderness at the site begin. The redness changes over two to three days to a bluish sinking patch of dead skin—the hallmark of necrosis. The wound heals slowly over months but usually completely. Rarely, bites may cause widespread symptoms, with occasional fatalities.

A spider bite, also known as arachnidism, is an injury resulting from the bite of a spider. The effects of most bites are not serious. Most bites result in mild symptoms around the area of the bite. Rarely they may produce a necrotic skin wound or severe pain.

Most spiders do not cause bites that are of importance. For a bite to be significant, substantial envenomation is required. Bites from the widow spiders involve a neurotoxic venom which produces a condition known as latrodectism. Symptoms may include: pain which may be at the bite or involve the chest and abdomen, sweating, muscle cramps and vomiting among others. Bites from the recluse spiders cause the condition loxoscelism, in which local necrosis of the surrounding skin and widespread breakdown of red blood cells may occur. Headaches, vomiting and a mild fever may also occur. Other spiders that can cause significant bites include: the Australian funnel-web spider and South American wandering spider.

Efforts to prevent bites include clearing clutter and the use of pesticides. Most spider bites are managed with supportive care such as nonsteroidal anti-inflammatory drugs (including ibuprofen) for pain and antihistamines for itchiness. Opioids may be used if the pain is severe. While an antivenom exists for black widow spider venom, it is associated with anaphylaxis and therefore not commonly used in the United States. Antivenom against funnel web spider venom improves outcomes. Surgery may be required to repair the area of injured skin from some recluse bites.

Spider bites may be overdiagnosed or misdiagnosed. In many reports of spider bites it is unclear if a spider bite actually occurred. Historically a number of conditions were attributed to spider bites. In the Middle Ages a condition claimed to arise from spider bites was tarantism, where people danced wildly. While necrosis has been attributed to the bites of a number of spiders, good evidence only supports this for recluse spiders.