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Over 3000 species of spiders can be found in North America, but relatively few are considered dangerous to humans. Spider venom is used to capture and kill small, but several spiders can cause toxic bites and can cause significant distress must be treated to obtain relief.

Luckily for us, most venomous spider bites, even those delivering dangerous neurotoxins, can be treated quickly with spider antivenin. However, 4 people die from a spider bite yearly in the USA.

This article shows 10 of North America’s deadliest species of spiders. The two most dangerous genera are the recluse spiders (Loxosceles) and widow spiders (Latrodectus), some of the most dangerous spiders in the world. There are 11 species of recluse Spiders and 32 species of widow spiders found in North America. 

If you have a shed, you probably have seen some spiders in there.  Do you know what else may be living there? Find out here

Wolf Spider
Jean and Fred Flickr CC 2.0

10. Wolf Spider

The wolf spider (Hogna carolinensis), found in North Carolina, is the largest among the wolf spider species in the US. Wolf spider bites are poisonous but not lethal. Wolf spiders are non-aggressive but can bite when provoked and should be considered dangerous to humans.

Adults grow just over 1 inch and are mottled gray to brown. The nocturnal wolf spider lives mostly outdoors in burrows, often around human habitation, such as garden areas.

Wolf Spiders are common throughout Canada and the US, including the Carolinas, Missouri, Texas, and California. The Kauai cave wolf spider in Hawaii has evolved to be eyeless.

Mouse spider
Jean and Fred Flickr CC 2.0

9. Mouse Spider

Mouse spider bites can cause severe illness, especially in small children. Although not typically aggressive, the male mouse spider (Scotophaeus Blackwall) attacks when provoked and is considered dangerous to humans. Their large, hard fangs deliver a deep and painful bite.

Mouse spiders can grow up to 1 and a half inches in body length. The male has a bright red head and elongated fangs with a brown or gray body. They burrow outdoors, usually more than 3 feet deep. The male is known to wander around on open ground, especially after it rains.

Mouse spiders have been spotted frequently in the US, mainly in the western states of Washington, Oregon, California, and Colorado.

Yellow sac spider
Dan Loarie Flickr CC 2.0

8. Yellow Sac Spider, Black Footed Spider

Several sac spider species exist in the US. Their bites deliver a mild toxin and can be painful, causing skin irritations such as erythema, edema, pruritis, and occasionally leaving behind dead tissue. However, the bites usually heal rapidly without noticeable scarring.

Yellow sac spiders (Cheiracanthium inclusum) are 1/4 to 3/8 inches in body length. They range from pale yellow to green, pink, or tan in color, with black chelicera.

Frequently found in or close to human dwellings, yellow sac spiders are often found building homes in curled leaves or crevices. Bites often occur when nocturnal creatures come across a sleeping human.

Yellow sac spiders are responsible for most spider bites found in the US. Their bites have been diagnosed across the continental US and even Hawaii.

Hobo spider
Tristan Loper Flickr CC 2.0

7. Hobo Spider

Hobo spiders (Tegenaria agrestis) deliver a dangerous venom, similar to recluse spiders. The bite leaves a sore red spot around the bite area, which can be painless initially. If left untreated, however, a blister typically develops on the site.

After 24-36 hours, the blister bursts, causing oozing ulceration. A severe headache, which can last up to a week, is the most common symptom. Vomiting, weakness, fatigue, temporary memory loss, and blurry vision can also follow.

Adult hobo spiders are brown and are 1/3 to 2/3 inches in body length. Males have more prominent mouthparts, shaped like boxing gloves, while females possess a larger abdomen.

Hobo spiders are typically found at ground level, rarely climbing vertical surfaces. They can be found with webs tucked into wall cracks or under woodpiles. Hobo spiders can be aggressive, sometimes biting without provocation.

Hobo spiders are principally found in arid climates, including Washington, Oregon, Idaho, Montana, Wyoming, Utah, and Colorado in the Northwestern US and the southwestern provinces of Canada.

You may know that insects have six legs and spiders have eight, but do you know all the other differences?  Find out more here.

Red widow
John Flickr CC 2.0

6. Red Widow Spider

The species listed #6 to #2 on this list are all part of the genus Latrodectus. They are arranged in terms of danger to human beings. 

Red widow spiders (Latrodectus bishopi) differ from others in the Latrodectus family. While venomous with antitoxin, similar to black widow spiders, the red widow, although not harmless to humans, is rarely known to cause serious harm since they live far away from human habitation.

True to their names, red widows have a red-orange back, a black abdomen with yellow rings, and vermillion red legs. The hourglass markings common among black and brown widows are missing, replaced by several red marks. They are typically about 1/2 inch in body length.

Red widow spiders are endemic to central and southern Florida. They live in areas where sand pine scrubs grow among dry dunes. Most of the time, they make their home in palmetto bushes at heights more than two feet off the ground. Red widows are a threatened species in the US.

brown widow
Roy Niswanger Flickr CC 2.0

5. Brown Widow Spider, Grey Widow Spider

The brown or grey widow spider (Latrodectus geometricus) carries a similar neurotoxin as the black widow but delivers less toxin. While painful, their bites affect only the immediate area and are less dangerous to humans.

Brown widow spiders are smaller and paler than black widows. Like others in the species, they have an hourglass-shaped marking on their abdomen, which are vivid orange or yellow. Unlike its relatives, the brown widow spider has a black-and-white geometric pattern on its abdomen’s dorsal side.

Brown widow spiders are found all over the continental US and Hawaii. Recent indications of this species overtaking black widow spiders in specific locales, including Southern California, are good news for humans since they pose less danger.

Northern black widow
Judy Gallagher Flickr CC 2.0

4. Northern Black Widow Spider  

While they deliver a potent venom that can cause nausea, pain, and sweating, there are typically no fatalities from the Northern black widow (Latrodectus variolus). Their bites are much less problematic than those from the Southern black widow Spider.

The Northern black widow is around 1 inch in body length with hourglass marks similar to the Southern Black Widow. They can be typically found around buildings in tropical areas.

This black widow species can be found along the Eastern Seaboard, from northern Florida to southern Canada.

Western black widow
Alan Moore Flickr CC 2.0

3. Western Black Widow Spider

Like the Northern black widow spider, the Western black widow (Latrodectus hesperus) can also deliver potent venom. This can cause nausea, pain, and sweating.  

The Western black widow spider is around 1 inch long with hourglass marks. They can be found in the western regions of North America, from Canada to Mexico.

The western black widow spider produces venom that contains a complex mixture of proteins and compounds. The venom is neurotoxic, affecting the nervous system of its prey or potential predators. In humans, a bite from a western black widow can also lead to neurotoxic effects. The venom primarily affects nerve transmission by interfering with the release of neurotransmitters, which are chemicals that allow nerve cells to communicate.

Southern black widow
Frank Boston Flickr CC 2.0

2. Southern Black Widow Spider

The Southern black widow (Latrodectus mactans) is a deadly species. Its painful bite delivers a neurotoxin, which is 15 times more harmful than that contained in the venom of a prairie rattlesnake. Even a tiny amount can cause headaches, nausea, pyrexia, abdominal pain, and hypertension. Vulnerable people, such as the very young, the elderly, and those with heart ailments, may require hospitalization. Fatalities are not uncommon. An effective antivenin is available, but medical attention should be sought as quickly as possible.

Southern black widows measure around 1/2 inch in body length. The female is more significant, shiny black, with a yellowish-orange or red hourglass-shaped mark on the abdomen’s underside. Some females tend to eat the male after eating, which has given the species its name. Females also deliver more venom than the male in a bite. These spiders seek shelter and are often found in basements and crawl spaces. They usually build nests close to the ground but have been known to spread their webs across plants.

Black Widows are found all over the world. The Southern black widow spider can be found in the U.S., Canada, Mexico, and the Caribbean.

brown recluse
Mike Keeling Flickr CC by-ND 2.0

1. Brown Recluse Spider

The brown recluse (Loxosceles recluse) is considered the deadliest among the 11 species of Loxosceles found in North America. Their venom can cause significant damage to subcutaneous tissue, leading to necrosis, and is thus considered very dangerous to humans. As their name suggests, recluse spiders are not always aggressive but will bite if threatened.

Ranging in size from 1/4 inch to 3/8 inches, the species is characterized by a dark violin shape at the top of its leg attachment. They are unique as they have six eyes instead of the usual eight found among spiders. They can live outdoors or indoors, withstand extreme temperatures, and survive long periods without food or water.

Brown recluses are found in a broad belt across the entire breadth of the USA over a 2000 km area, covering part or all of Nebraska, Kansas, Oklahoma, Texas, Louisiana, Arkansas, Missouri, Kentucky, Tennessee, Mississippi, Alabama, Georgia, Ohio, Indiana, Illinois, and Iowa.

The brown recluse spider is not found in Hawaii, but its relative, the brown violin spider, lives on the islands. About an inch long, the violin mark is located on the combined head and midsection. They live in rocks or woodpiles or under boards or bark.

References And Further Reading

  1. “Common Spiders of North America” by Richard A. Bradley This book offers comprehensive information about various spider species found in North America, including those that are potentially dangerous. It covers their identification, behavior, and venomous properties.
  2. “National Audubon Society Field Guide to North American Insects and Spiders” by National Audubon Society This field guide includes a section on spiders, covering their identification, habits, and distributions. It provides insight into the characteristics of dangerous spiders.
  3. “Spiders of North America: An Identification Manual” by Darrell Ubick, Pierre Paquin, Paula E. Cushing, and Vincent Roth While this book covers a wide range of spider species, it includes information about dangerous spiders found in North America and their distinguishing features.
  4. “Venomous Creatures of North America” by Roger Caras Although not solely focused on spiders, this book provides insights into various venomous animals, including spiders, found in North America.
  5. “Spiders of the Eastern United States: A Photographic Guide” by W. Mike Howell and Ronald L. Jenkins While centered on the eastern United States, this guide offers detailed photographs and descriptions of spiders, including those that are potentially dangerous.