Over 3000 species of spiders can be found in North America but relatively few of these are considered dangerous to humans. Spiders’ venom has evolved to enable the capture and killing of smaller prey and not large mammals like us. Having said that, there are several spiders whose toxic bites can cause significant distress and 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, an average of 4 people die from a spider bite every year in the USA.
In this article, I look at 10 of the deadliest species of spiders found in North America. The two most dangerous genus are the Loxosceles (Recluse Spiders) and Latrodectus (Widow Spiders). There are 11 species of Recluse Spiders and 32 species of Widow spiders found in North America.
This post contains photos of each spider in the list. Do not read on if you dont want to look at photos of spiders.
10. Wolf Spider
The wolf spider (Hogna carolinensis) found in North Carolina, is the largest among the wolf spider species found 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. The bites can be very painful.
Adults can grow just over 1 inch in body length and are mottled gray to brown. Their distinctive look comes from a Union Jack impression on its back. 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.
9. Mouse Spider
Mouse spider bites can cause severe illness, especially in small children. Although not normally aggressive, the male mouse spider (Scotophaeus blackwalli) attacks when provoked and is considered dangerous to humans. Their large, hard fangs deliver a deep and painful bite.
Mouse spiders can grow large, up to 1 and 1/2 inches in body length. The male has a bright red head and elongated fangs, to go with a brown or gray body. They burrow into the ground outdoors, frequently going more than 3 feet deep. The male is known to wander around on the open ground, especially after it rains.
Mouse spiders have been spotted frequently in the US, mostly in the western states of Washington, Oregon, California, and Colorado.
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 and pruritis, and occasionally leaving behind dead tissue. However, the bites usually heal rapidly, without pronounced 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. They are
frequently found in or close to human dwellings, building homes in curled leaves or crevices. Bites often occur when the nocturnal creatures come across a sleeping human.
Yellow sac spiders are responsible for the majority of spider bites that are found to occur in the US. Their bites have been diagnosed across the continental US and even Hawaii.
7. Hobo Spider
Hobo spiders (Tegenaria agrestis) deliver a dangerous venom, similar to those of recluse spiders (see below). The bite leaves a sore red spot which can be painless initially. If left untreated, however, a blister typically develops on the spot.
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. Nausea, weakness, fatigue, temporary memory loss, and blurry vision can also follow.
Adult Hobo Spiders are 1/3 to 2/3 inches in body length and are brown. Males have larger mouthparts, shaped like boxing gloves, while females possess a larger abdomen.
Hobo spiders are typically found at the 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 dry and arid climates, including the states of Washington, Oregon, Idaho, Montana, Wyoming, Utah, and Colorado in Northwestern US and the southwestern provinces of Canada.
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 in several ways. While venomous with antitoxin similar to that delivered by the black widow spiders (see below), the red widow is rarely known to cause serious harm to human beings, since they live far away from human habitation.
Red widows, true to their names, have a red-orange back, with an abdomen that is black 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 inches 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.
5. Brown Widow Spider, Grey Widow Spider
The brown or grey widow spider (Latrodectus geometricus) carries a similar neurotoxin as the black widow (see below) but delivers less toxin. Their bites, while painful, typically affect only the immediate area and are therefore 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 its abdomen. However, the markings in these species are a vivid orange or yellow. Unlike its relatives, the brown widow spider has a black and white geometric pattern on the dorsal side of its abdomen.
Brown widow spiders are found all over the continental US, as well as Hawaii. There have been recent indications of this species overtaking black widow spiders in certain locales including Southern California, which is good news for humans since they pose less danger.
4. Northern Black Widow Spider
While they deliver a potent venom that can cause nausea, pain, and sweating, there are typically no fatalities that occur from bites of these two species. In general, their bites are much less problematic than those from the Southern black widow Spider (see below).
The Northern black widow (Latrodectus hesperus) is a venomous spider. They are a different species to the Western black widow and the Southern black widow.
The Northern black widow is around 1 inch in body length with hourglass marks similar to the Southern Black Widow (see below). They can be typically found around buildings in tropical areas.
This species of black widow spider can be found along the Eastern Seaboard, from northern Florida to southern Canada.
3. Western Black Widow Spider
Very similar to the Northern black widow spider, the Western black widow (Latrodectus variolus) can also deliver a potent venom. Again this can cause nausea, pain, and sweating.
The Western black widow spider is around 1 inch long with hourglass marks.
The Western black widow spider is found in the western regions of North America, from Canada to Mexico.
2. Southern Black Widow Spider
The Southern black widow (Latrodectus mactans) is truly a deadly species. Its painful bite delivers a neurotoxin which is 15 times deadlier than that contained in the venom of a prairie rattlesnake. Even a small amount can cause headaches, nausea, pyrexia, abdominal pain, and hypertension. Vulnerable people, such as the very young, elderly, and those with heart ailments may require hospitalization. Fatalities are not uncommon. Luckily, an effective antivenin is available for use, but medical attention should be sought as quickly as possible.
Southern black widows measure around 1/2 inches in body length. The female is larger, shiny black with a yellowish-orange/red hourglass-shaped mark on the underside of the abdomen. The tendency of some of the females to eat the male after eating has given the species its name. The female also delivers much 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 is common within the US, Canada, and Mexico, as well as the Caribbean.
1. Brown Recluse Spider
The brown recluse (Loxosceles reclusa) 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 to be very dangerous to humans. As their name suggests, recluse spiders are not always aggressive, but they will bite if threatened.
Ranging in size from 1/4 inches to 3/8 inches, the species is characterized by a dark violin shape at the top of its leg attachment, with the neck pointing towards the abdomen. They also have six eyes instead of the normal 8 found among spiders. They can live outdoors or indoors and can 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, its violin mark is found on the combined head and midsection. They live in rock or woodpiles, or under boards or bark.
Bites from spiders can range from painful but with no lasting damage, to ones that can cause severe damage and even death. In general, it is best to get medical treatment at the first sign of symptoms typically associated with a spider bite – it may end up saving your life.