Spider-Man: 5 Weird Effects of Real Spider Bites
The Brazilian wandering spider seeks out its prey.
Credit: Nashepard | Shutterstock

Although Spider-Man got his superhero abilities from a spider bite, ordinary spider-bite victims may have to deal with spider-bite effects that have nothing to do with being able to scale walls and climb around on ceilings.

Some of the weirdest effects that spider venom may have on regular, nonsuperhero humans include unwanted erections, dead skin tissue that turns black, unusual rashes, dark pee and sweat so heavy it makes puddles on the floor.

However, it is important to remember that such unusual symptoms are extremely rare, and the vast majority of spider bites are harmless, or cause only mild irritation and itchiness. [In Photos: The Science of the Amazing Spider-Man 2]

In fact, spiders do not often bite people, and if they do, it is because they feel threatened. Black widow spiders and brown recluse spiders are the only two spider species in North America whose bites may sometimes result in symptoms more serious than minor local pain and swelling, according to Rick Vetter, a retired arachnologist at the University of California, Riverside.

Although hobo spiders, which are common in the Pacific Northwest, are also listed by the Centers for Disease Control and Prevention as one of the three types of spiders that can be toxic to people, some researchers have argued that hobo-spider venom may not be so toxic after all.

Here are some of the weirdest effects spider bites have had on people.

Venomous Viagra?

The Brazilian wandering spider's venom contains a toxin whose unusual erection-inducing qualities have attracted the attention of the pharmaceutical industry. In 2007, researchers found that the bites of the Brazilian wandering spider can cause long and painful erections in human males, along with other symptoms. The effect happens because the spider's venom raises the levels of nitric oxide, which is a chemical that increases blood flow.

Researchers have since tested the toxin that is responsible for this unusual effect, called PnTx2-6, in the hope of developing a potential new drug for erectile dysfunction.

The Brazilian wandering spider is large, with a body size reaching up to 2 inches (5 centimeters) and leg spans stretching 5 or 6 inches (13 to 15 cm). Although the creepy crawler's size may make it look threatening, it is not aggressive and, like most spiders, will only attack when it feels threatened, experts say.

Dead tissue

Although there have been cases of "necrotic arachnidism," in which spider venom kills human tissue, such cases are extremely rare. In fact, researchers estimate that less than one case of dead human tissue is reported per 5,000 spider bites from verified spider specimens, and verification of spider bites is very rare, Dr. Scott Weinstein, a toxinologist at Women's and Children's Hospital in North Adelaide, South Australia, told Live Science. (Toxinology is the study of the venoms and poisons of plants, animals and microbes; it is different from toxicology, which is the study of chemicals and drugs as they affect the body.)

If a spider bite is "verified," it means that there was actual evidence that a person was bitten by a particular kind of spider. The only spider in North America whose bites have been shown to kill human tissue in rare instances is the brown recluse spider, Vetter said.

When necrosis does occur, tissue may sometimes turn black as cells die. One such case was reported last year — a woman on vacation in Italy developed necrosis in her ear after being bitten by a brown recluse spider. Part of her ear turned black, and her doctor had to remove the dead tissue and restore it, using cartilage from the woman's ribs.

Weird rash

Some people develop unpredictable skin reactions to spider bites. A 66-year-old patient in France developed a strange rash after being bitten by a spider, which the doctors suspected was likely a brown recluse spider, according to a report of his case. The man had pinhead-size bumps on his forearms, which later spread to other parts of his body.

The medical staff diagnosed the man with a condition called acute generalized exanthematous pustulosis (AGEP), which typically occurs in people taking antibiotics. Other reports have also linked AGEP to brown recluse spider bites, the researchers said. The man recovered in five days, after doctors treated him with oral corticosteroids.

Unusual blood disorders and dark pee

In the case of the man in France who developed the strange rash, the doctors also found that he had a blood disease called periarteritis nodosa (PAN), in which small arteries become swollen and damaged. The doctors linked his blood condition with the brown recluse bite, because previous reports had described conditions similar to PAN in animals injected with brown recluse spider venom.

In fact, blood disorders are some of the rare symptoms that occur in people who have been bitten by recluse spiders, Vetter wrote in one study. The brown recluse venom may cause red blood cells to burst and release their contents into plasma, in a process called hemolysis. As a result, anemia may develop and can last from four to seven days, he said.

These blood problems may lead to other symptoms, such as acute kidney injury and jaundice (yellowing of the skin), as the blood protein called hemoglobin breaks down. The waste products of the breakdown can build up in the blood, and turn the urine dark when they are then excreted.

Puddles of sweat

Some Australian widow spider bite victims have been found to sweat so much after getting bitten that their sweat formed puddles on the floor, Vetter reported in one study.

Excessive sweating is one of the symptoms that may result from the bites of certain spiders that affect the nervous system. The venom of the black widow, for instance, attacks nerves by blocking their signals to the muscles. This causes the muscles to contract repeatedly, which can be painful and stressful for the body.

Black widow spider bite victims may also experience other nerve-related symptoms, such as high blood pressure, restlessness and severe facial spasms.

Who gets these spider-bite symptoms?

Whether a spider bite affects a person only mildly or causes severe symptoms depends on a number of factors, such as the amount of the venom injected, and the size and age of the person who got bitten. Children and elderly people are particularly susceptible to extreme symptoms from toxic spider bites.

However, most people who get bitten are highly unlikely to experience these severe symptoms, researchers say.

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