9 of the World’s Deadliest Spiders

More than 43,000 different species of spiders are found in the world. Of these, only a small number are considered dangerous to humans, with fewer than 30 responsible for human deaths. This discrepancy is largely due to the size difference between humans and spiders. Spider venom is designed to work on smaller animals. However, the venom of some species can cause skin lesions in humans or trigger allergic reactions that may lead to fatalities. It is important to note that “death by spider bite” is incredibly rare, as clinics, poison control centers, and hospitals often stock various species-specific antivenoms to treat bites effectively.

Brown Recluse Spider (Loxosceles reclusa)

Close-up image of a Brown recluse spider

The brown recluse spider is widely regarded as one of the most dangerous spiders in the United States. Its venom possesses a destructive property that breaks down the walls of blood vessels near the bite, often leading to a large skin ulcer. A 2013 study revealed that a specific protein in the spider’s venom targets phospholipid molecules, which are crucial components of cell membranes, converting these molecules into simpler lipids. The resulting wound may take several months to heal and is susceptible to infection, which can, in some cases, lead to death. However, fatalities from brown recluse spider bites are rare.

Most brown recluse spiders, sometimes called violin spiders due to the distinct violin-shaped marking on their cephalothorax, are found in the western and southern United States. These spiders are generally small, measuring around 0.25 inches in length with a leg span of approximately one inch. They seek refuge in secluded areas, including caves, rodent burrows, and other protected environments, as well as undisturbed spaces within buildings like attics, storage areas, and wall or ceiling voids.

Brazilian Wandering Spiders (Phoneutria fera and P. nigriventer)

An educational video about swallowing spiders in your sleep

These spider species are often called banana spiders because they are commonly found on banana leaves. They are known for their aggressive defense posture, characterized by raising their front legs straight up in the air. Phoneutria spiders are venomous to humans and are considered among the deadliest spiders globally. Their venom affects the nervous system, causing various symptoms such as salivation, irregular heartbeat, and priapism (prolonged, painful erections) in men. Interestingly, scientists are currently researching the venom of P. nigriventer as a potential treatment for erectile dysfunction.

A notable incident in late 2013 involved a family in London, England, who were forced to evacuate their home for fumigation due to an infestation of tiny Brazilian wandering spiders. The infestation originated from an egg sac deposited in a banana bunch that was shipped to the family’s local grocery store, highlighting the potential dangers of these spiders.

Yellow Sac Spider (Cheiracanthium inclusum)

Yellow sac spiders belong to the Clubionids family, a group of spiders known for building silken tubes under stones, in leaves, or grass. They are typically small, ranging from 0.12 to 0.6 inches in body length. The species Cheiracanthium inclusum is found throughout the United States, Mexico, and parts of South America, and is known for its venomous bite, often encountered indoors.

These spiders release a cytotoxin venom that can, in some cases, cause necrotizing lesions. While such lesions are rare, redness and swelling at the bite site are common reactions. Yellow sac spiders are not known for their docility; females, in particular, may bite when defending their eggs.

Wolf Spider (family Lycosidae)

Wolf spiders, members of the Lycosidae family, represent a large and diverse group of spiders found worldwide. These spiders, named for their wolf-like hunting style of chasing and pouncing on prey, are known for their running speed. They are typically found in grassy areas or under stones, logs, or leaf litter. However, they can also find their way into human dwellings in search of insects.

While not considered aggressive, wolf spiders will bite in self-defense. Although venomous, their bites are generally not dangerous to humans. However, some individuals with allergies to spider bites may experience nausea, dizziness, and an elevated heart rate. The spider’s large fangs can cause physical trauma at the bite site, which can be painful, often compared to a bee sting.

Black Widow Spider (Latrodectus mactans)

Black widow spider against a white background

The black widow spider is notorious for its venomous bite, resulting in over 2,500 visits to poison control centers annually in the United States. This spider species is found throughout the United States, parts of Canada, Latin America, and the West Indies, inhabiting various settings such as woodpiles, burrows, and among plants.

Female black widows, typically around one inch in length, are recognizable by their shiny black bodies and the distinctive reddish to yellow hourglass design on the underside of their abdomens. Males, on the other hand, are significantly smaller and are characterized by pairs of red and white stripes on the sides of their abdomens.

While a black widow bite may feel like a pinprick, it often leads to severe muscle pain and cramping, nausea, and mild paralysis of the diaphragm, making breathing difficult. While most victims recover without serious complications, the bite can be fatal to very young children and the elderly. However, no deaths have been attributed to black widow spider bites in the United States.

Brown Widow Spider (Latrodectus geometricus)

Brown widow spider on a white background

Believed to have originated in Africa, the brown widow spider has become an invasive species in other parts of the world, including southern California, the Caribbean, the U.S. Gulf Coast, Japan, South Africa, Madagascar, Australia, and Cyprus. These spiders often seek shelter in buildings, old tires, under automobiles, and among shrubs and vegetation.

Brown widows, as their name suggests, have a brownish appearance, ranging from tan to nearly black. Their abdomens often feature ornate markings in dark brown, black, white, yellow, or orange. One distinguishing feature that sets them apart from other widow spiders is the orange hourglass marking on the underside of their abdomens.

Although the brown widow’s venom is considered twice as potent as that of the black widow, the species is not aggressive and injects only a tiny amount of venom when it bites. Despite this, brown widow bites were linked to the deaths of two individuals in Madagascar in the early 1990s.

Red Widow Spider (Latrodectus bishopi)

The red widow, also known as the red-legged widow, is another venomous spider species. Distinguished by its reddish cephalothorax and legs, this spider has a reddish-brown to black abdomen. Many red widows also sport a red mark on the underside of their abdomen, which can be hourglass-shaped, triangle-shaped, or indistinct.

Red widow spiders primarily inhabit palmetto-dominated scrublands in central and southern Florida. These spiders feed on insects and are not considered aggressive towards humans. However, they have been known to bite when protecting their eggs or when trapped against a person’s skin by clothing.

A red widow bite produces symptoms similar to those of a black widow bite, including pain, cramping, and nausea. Fatalities are rare, as the spider injects a minimal amount of venom. However, very young children, the elderly, and individuals with underlying health issues are most vulnerable to red widow spider bites.

Redback Spider (Latrodectus hasselti)

Related to the black widow spider, the redback spider is less widespread. While native to Australia, this species has spread to New Zealand, Belgium, and Japan through grape exports, as they often create nests and webs on grape leaves and within bunches. The redback spider is prevalent throughout Australia, thriving in all environments except for the hottest deserts and the coldest mountaintops.

Redback spiders are recognizable by their prominent red stripe or hourglass-shaped mark on their black backs, a feature more noticeable in females. These spiders are not aggressive and often feign death when disturbed. However, females defending their eggs are highly likely to bite. Bites can also occur when the spider crawls into shoes or clothing and becomes trapped against the skin.

Both male and female redbacks are venomous. However, most envenomations result from female bites. The venom, a cocktail of neurotoxins known as alpha-latrotoxins, can cause pain, sweating, rapid heartbeat, and swollen lymph nodes. The severity of symptoms often depends on the amount of venom injected.

Funnel-web Spiders (family Dipluridae)

This spider family, belonging to the order Araneida, gets its name from their distinctive funnel-shaped webs. They patiently wait for prey to come into contact with their webs and then swiftly capture the insect at the funnel’s mouth.

The species Atrax robustus and A. formidabilis, large, brown, bulky spiders found in southern and eastern Australia, are particularly notorious for their venomous bites. Several human deaths have been recorded in the Sydney area since the 1920s due to bites from these aggressive spiders. Fortunately, an effective antivenom for the primary toxin in their venom has been developed, significantly increasing the chances of survival if administered quickly after a bite.