Venomous Spiders in North America

Venomous spiders in North America

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With their eight creepy legs and almost alien-like appearance, spiders are one of the most feared creatures in the world! All spiders are venomous in one way or another, as this is largely how they catch their prey. But not all species are venomous to humans.

The concept of being bitten by a spider is, for many people, what frightens them about these otherwise amazing creatures. In North America, there are around 3400 spiders, but not all of them will cause you harm.

Are all Spiders Venomous?

Are all spiders venomous?
Black Widow Spider (Latrodectus mactans) – One of the Most Venomous Spiders in North America

Before we get into the nitty-gritty of whether spiders are venomous or not, there is one thing it pays to remember; spiders are not usually aggressive towards humans. The only time that they will actively attack you is if they feel threatened. Otherwise, most spiders will just go about their eight-legged business and leave you well alone.

However, we do have to also keep in mind that pretty much every species of spider has some degree of venom. All, apart from two species in the Uloboridae family, have venom glands but there aren’t too many spiders whose venom is seriously harmful to humans.

A lot of people are of the mindset that giant hairy tarantulas are the most dangerous arachnids to humans. But this isn’t the case. In fact, these gentle giants are unlikely to cause you any more harm than a bee sting.

How Do Spiders Inject Their Venom?

How do spiders inject their venom?
Close-Up of a Huntsman Spider with its Chelicerae Visible

All but two spiders have venom glands that are designed to produce venom that the spider uses to immobilize its prey. That said, it is believed that these glands first adapted in order that the spider could externally digest its prey.

The venom glands are located under the carapace or in the chelicerae, which is a set of pointy jaws at the front of the spider’s mouth. Here, there are also a set of fangs that usually remain inside the jaw. But when the spider catches its prey, it will release the fangs, which act like a hypodermic needle, injecting venom into the unfortunate victim.

Spider anatomy - the venom glands are located under the carapace or in the chelicerae

When the venom gets to work, it will paralyze the prey which makes it a lot easier and safer for the spider to feed as there won’t be a struggle. The venom also preserves the prey should the spider wish to eat it later on.

Types of Spider Venom

Blackwidow spiders carry neurotoxins that are 15 times more potent than that of a rattlesnake
Black Widow Spiders Possess Neurotoxins that are 15 Times more toxic than that of a Rattlesnake

There are two main types of spider venom; neurotoxic and necrotic. Most spiders will possess one of the two, although there are species that have both. What’s amazing is that scientists believe that there could be as many as 10 million different toxins present in spider venom, with each spider possessing at least 100 of these!

Which toxins and which type of venom any given spider has will vary according to its habitat and the type of prey it catches.

Necrotic/Cytotoxic Venom

Necrotic venom attacks the skin and tissue around the area that has been bitten. It does this by causing damage to the cells. The level of damage varies depending on the spider, but it could be something as simple as a blister or inflammation right through to death of the tissue, known as necrosis.

As well as this, in more serious cases, the damage can become very intense, with wounds spreading and potentially becoming gangrenous. For some victims, the healing process can take years, and there is a high risk of severe scarring.

Most spiders from the Sicariidae family possess a type of necrotic venom including the feared recluse spiders.

As well as localized tissue damage, victims of a necrotic venom bite may suffer secondary symptoms such as kidney failure and even death.

Neurotoxic Venom

Spiders that deliver neurotoxic venom affect your nervous system. This is used to paralyze prey, but when potent enough, can do some harm to humans.

The main way that these toxins work is by blocking the nerves to the muscles, which can result in cramps, stiffness, and of course, paralysis. However, since the production of neurotransmitters is massively over-stimulated, this can cause more severe symptoms such as respiratory failure and an abnormal heart rate.

Widow spiders, Brazilian wandering spiders, and the infamous Australian funnel-web spider possess some of the most powerful neurotoxic venoms on the planet! In the very worst cases, fluid can collect in the lungs, which have the potential to kill a human victim.

What Do Spiders Use Their Venom For?

What do spiders use their venom for?
Female Adult Brown Widow Spider (Latrodectus geometricus) with it’s Prey

While there is some suggestion that spiders developed venom glands to aid with digestion, this theory is disputed. But we do know that spiders use digestive fluids which they ‘vomit’ onto or into their prey to begin digestion outside of the body. They then consume the resulting fluid along with some solid parts of their prey.

Nonetheless, we also know for certain that spiders use their venom in two main ways. Primarily, it is used during hunting and feeding. Spiders are carnivores and, depending on the species, will hunt everything from small flies and insects through to birds and small mammals or reptiles.

When catching their prey, spiders will inject venom to immobilize them so that there won’t be a struggle. On top of this, if the spider doesn’t want to consume their meal until later on, their venom helps to preserve it.

Spiders may also use their venom as a defense mechanism when they are threatened. Believe it or not, many animals will hunt and prey on spiders such as birds, toads, monkeys, and scorpions, among others.

To protect themselves, spiders will inject a certain amount of venom if they are touched, restrained, or suddenly disturbed. Interestingly, they have the ability to control the amount of venom and in some cases, may not release any at all; the bite itself may be enough to warn off a predator.

U.S. Spiders that have Potent Venom

The varying terrain and climate across the United States means that there are suitable habitats for a wide range of spiders. Here, you will find more than 3400 species of spiders, but only a small handful are very dangerous to humans.

1. Brown Recluse Spider (Loxosceles reclusa)

Brown Recluse Spider (Loxosceles reclusa) is most active at night when it comes out to hunt

The brown recluse spider is most active at night when it comes out to hunt. However, it’s not uncommon for them to meet with humans. But there’s no real need to be worried because these aren’t the most aggressive venomous spiders in the USA. They do produce a necrotic venom but can be easily identified so you can keep them at arm’s length.


One of the most obvious ways to tell if you have a brown recluse spider is to look at its markings. Mature specimens will more often than not have a violin-shaped marking on the cephalothorax. However, it is important to note that this can vary between individuals.

Another good way to identify the brown recluse spider is to look at the coloration of the legs which are almost always uniform without stripes, spots, or other markings.

These spiders, unlike most others, have three pairs of eyes on the forehead, which is one of their most distinguishing features and a reliable way to tell them apart from other spider species.


The brown recluse spider can often be found inside homes where it will hide underneath furniture, in bedrooms and bathrooms, and in the attic.

When found outdoors, these spiders like to hide underneath rocks as they like to be concealed. You may find them in your garage or garden shed.


The brown recluse spider is generally found across 16 of the United States which include:

  • Alabama
  • Arkansas
  • Georgia
  • Illinois
  • Indiana
  • Iowa
  • Kansas
  • Kentucky
  • Louisiana
  • Mississippi
  • Missouri
  • Nebraska
  • Ohio
  • Oklahoma
  • Tennessee
  • Texas

That said, there have been reports of cases of these spiders being present in places like Southern California, Florida, the District of Columbia, and Pennsylvania, although they are not common in these places.

Bite Symptoms

The symptoms of a bite from a brown recluse spider may include:

  • Pain
  • Pus filled blister eight hours after receiving the bite
  • Fever
  • Difficulty sleeping
  • Redness
  • A hard lump at the bite site
  • Skin grafts may be required for necrosis in very severe cases

2. Black Widow Spider (Latrodectus mactans)

Black Widow spiders (Latrodectus mactans) have an hourglass-shaped red marking on the abdomen

While a lot of people see the black widow as an aggressive spider species, it really isn’t. Usually, these spiders are only temperamental when they are guarding their egg sacs.  Although when they bite, it’s a good idea to seek immediate medical attention as they are one of the most venomous spiders in North America. Amazingly, these spiders pose the greatest risk to humans in terms of receiving a venomous bite across the western parts of the country.


The black widow is perhaps one of the most easily identifiable spiders on this list, with a black, round body that’s shiny and never hairy. These spiders also have an hourglass-shaped red marking on the abdomen. They’re usually around half an inch in size with the males being slightly smaller.


You will find the black widow spider in dark and damp areas, including the crawl space under your house. They like to live in wood piles and under rocks as well as in garden sheds.


One of the most widely distributed spiders, black widows can be found in all states from southern New England down to New Mexico.

Bite Symptoms

  • Pain
  • Vomiting
  • Fever
  • Breathing difficulties
  • Muscle spasm
  • Chills
  • Increase in blood pressure
  • Sweating
  • Delirium

Please note that the bite from a black widow will often require medical attention so seek this urgently if you are bitten.

3. Red Widow Spider (Latrodectus bishopi)

Red Widow Spider (Latrodectus bishopi) has red spots that are outlined with white and appear all over the spider’s back
Florida Division of Plant Industry Archive / Wikimedia Common / CC BY 3.0 US

Our next eight-legged critter is the red widow spider which is sometimes called the red-legged widow. This species is incredibly beautiful with distinct markings that make it a prized spider for those that collect them.

There are almost no deaths reported from the red widow spider since this is a non-aggressive species. When it does bite, it only injects a very small amount of venom, so symptoms are typically mild.


You can instantly tell a red widow apart from other spiders thanks to its obvious red spots that are outlined with white and appear all over the spider’s back. On the underside there is a triangular red marking, and the rest of the body is black. The head and the legs are either red or orange in color.


Red widows like to live in scrublands, and this is where they are almost exclusively found.


The red widow spider is endemic to Florida. However, there are reports from scientists that the range of this species looks set to spread.

Bite Symptoms

The symptoms you will experience from a red widow bite will be largely the same as those from a black widow. Please refer to bite symptoms for the black widow spider above.

4. Brown Widow Spider (Latrodectus geometricus)

Brown Widow Spider (Latrodectus geometricus) has a very similar appearance to the black widow in terms of it’s body shape

The brown widow spider is native to South Africa. However, it is thought that it was first introduced to the United States from somewhere in South America. This spider is now common throughout the world and in many places is considered to be an invasive species.

While these spiders are not generally aggressive towards humans, their venom is twice as potent as that of their cousin, the black widow. 


The brown widow spider has a very similar appearance to the black widow in terms of it’s body shape. However, rather than being black, these spiders range in color from tan to dark brown and they have an orange hourglass shape on their body. Additionally, some species of brown widow will also have ornate markings across the body, which can be orange, white, or black.


You’ll find the brown widow hiding under furniture and boxes and anywhere that it can take cover. It’s not uncommon for them to set up home in an old tire, but they prefer tropical climates.


The brown widow spider is found across all of the southwestern United States. They are also common in southern California and are as far spread as the Caribbean nations.

Bite Symptoms

As with the red widow spider, the symptoms of the brown widow are typically the same as the black widow, so please refer to the symptoms for the black widow spider above for more information.

5. Hobo Spider (Tegenaria agrestis)

Hobo Spider (Tegenaria agrestis) tend to live in fields or woodlands, but they may also be found hiding under rocks and stones

Scientifically known as tegenaria agrestis, many people think that this means the hobo spider is an aggressive species. However, the name refers to the fact that these spiders like to live in fields (agricultural land.) That said, they can become aggressive if they are provoked, but the good news is that, while they possess cytotoxic venom, necrosis is rare. Moreover, since 2017, the CDC stopped listing the hobo spider as a venomous species to humans. 


One of the most distinguishing features of the hobo spider is its long hairy legs. The body usually grows up to about half an inch and the spider is brown in color. You’ll notice that these creepy crawlies have a distinct chevron like pattern on their backs and that the males have mouthpieces that don’t look that dissimilar to a boxing glove; if you’re brave enough to get that close!


Hobo spiders tend to live in fields or woodlands, but they may also be found hiding under rocks and stones. It’s not likely that you’ll find one in your house since they are often seen off by competing species such as the giant house spider.


The hobo spider is common throughout Asia and Europe, but it’s also found across North America, particularly in the western states, and is most concentrated in the Pacific Northwest.

Bite Symptoms

  • Pain at the bite site
  • Inflammation
  • Muscle aches
  • Joint aches
  • Tissue necrosis, although this is rare

6. Wolf Spiders (family Lycosidae)

There are around 240 species of wolf spider (family Lycosidae)

There are around 240 species of wolf spider, of which, around 125 reside in the United States. One of their most notable traits is that they are incredibly fast runners. While this can be frightening to some people, keep in mind that they’re very beneficial to humans because they feed on a lot of crop pests. Moreover, wolf spiders are very docile and only bite if they are mishandled.


The wolf spider is sometimes confused with the brown recluse, but since they’re more often in contact with humans, if you see a hairy brown spider, it’ll likely be a wolf spider.

Their bodies grow up to an inch, and their legs are about the same length, so they’re quite large. That said, the legs are rather stout compared to other species.


You’ll often find wolf spiders underneath rocks and stones, hiding in the grass or among leaf litter, and in log piles. They don’t typically tend to come into the house unless there is a significant insect presence that they can prey upon. In the wild, various species of wolf spiders are found in rainforests, deserts, wetlands and many other locations.


The wolf spider is common right across the world and all over North America.

Bite Symptoms

The bite from a wolf spider is not considered to be life-threatening and more often than not, won’t require medical attention. However, you may experience the following symptoms:

  • Pain
  • Swelling
  • Redness
  • Wound infection
  • Swollen lymph nodes resulting from infection

7. Black-Footed Yellow Sac Spider (Cheiracanthium inclusum)

Black-Footed Yellow Sac Spider (Cheiracanthium inclusum) is responsible for more human bites than any other spider species in the USA

It is thought that the black-footed yellow sac spider is responsible for more human bites than any other spider species in the USA. However, the symptoms are usually mild, and it’s more likely that you’ll have an allergic reaction than die from the venom. 

These spiders produce a necrotizing venom but are generally not aggressive unless it’s during mating season and the females are guarding their egg sacs.


The black-footed yellow sac spider is a light-colored creature that is said to take its color from the last thing it ate. Most people notice their feet first if the spider is on a light-colored surface, as they are distinctly darker than the rest of the animal. These spiders can grow to anywhere between 0.12 inches and 0.60 inches.


Black-footed yellow sac spiders can be found around the home where they often hide in shoes and clothing. This is where most people will come into contact with them, but they’ll also hide in other indoor spots, such as behind boxes.

These spiders make silk tubes under the grass, leaf litter, and stones which is where you’ll commonly find them outdoors.


You will find the black-footed yellow sac spider all over the United States. This species is also very common in Mexico and throughout South America.

Bite Symptoms

  • Itching
  • Redness at the bite site
  • Some sensitive individuals may experience allergy-like symptoms which can range from mild to severe

8. Huntsman Spider (Heteropoda venatoria)

Huntsman (Heteropoda venatoria) are large spiders whose leg spans can reach up to 4.8 inches

The huntsman spider is a very large species and has a similar appearance to the brown recluse which is why so many people mistake it for that species. It’s often referred to as the giant crab spider but while they’re big and scary looking, they’re not very aggressive and bites to humans are rare.

The females can lay up to 200 eggs in a sac and the huntsman spider is known for its ability to move at super speeds, especially when it is disturbed.


Potentially the most frightening thing about the huntsman spider is its appearance. These are large spiders whose leg spans can reach up to 4.8 inches. They have brown coloration with black spotted markings on the legs in both males and females.

The body is flat which is why the spider is easily able to get into crevices and cracks that may look as though they are far too small for this eight-legged friend to fit into.


Huntsman spiders can be found hiding around the home or are sometimes bold enough to just sit on the wall. However, they’re also common hiding in sheds, garages, and outbuildings, and have adapted very well to living in human settings.


Huntsman spiders are common in many areas of the world. They’re probably most well known for living in Australia but are also found in North America where, in Florida, they have become wild owing to the fact that there is no frost. The huntsman is unable to survive in freezing temperatures.

Bite Symptoms

  • Pain
  • Swelling
  • Headache
  • Vomiting
  • Increased heart rate

How to Prevent Spider Bites?

How to prevent spider bites?

With more than 47,000 species of spider currently known to humans, they’re a creature that we have to learn to coexist with. While most species are docile and won’t attack humans for no reason, they will defend themselves if necessary. Here are some points on how to avoid being bitten.

  • Use sticky traps to catch spiders if you have significant numbers in your home.
  • Do not place beds against the wall, and ensure that there are no overhanging sheets or any items under the bed. This makes it difficult for the spiders to get onto the bed and bite you while you’re sleeping.
  • Any items that are in storage in sheds or outbuildings should be properly sealed. Keep things in zippered plastic bags and seal all cardboard boxes with tape. If you have to put your hands into a bag or box, this will eliminate the risk of a spider being inside.
  • Check clothing and shoes for spiders before putting them on. Spiders may have crawled inside items left on the floor during the night.
  • Some spiders, like the recluse, love clutter so make sure to minimize this around the home.
  • Keep your wood piles away from the main house. Should spiders set up home here, they will likely move into the main house if the wood pile is leaning against it.
  • Keep your home clean, vacuumed, and tidy to make it less attractive to spiders.
  • Use insect screens and well-sealed windows to keep spiders out.
  • Use insecticides and spider repellents around entrances to your home including any cracks and crevices that a spider might use to get in.
  • Keep grass and foliage trimmed back around the house to ensure as few spider habitats as possible. The less you are in contact with them, the less chance there will be of being bitten.
  • If you need to remove spiders by handling them, wear gloves for protection. If you need to remove one from your person, brush it away rather than squash it as it’ll be more likely to bite when crushed.

What to Do if You Get Bitten by a Spider?

How to treat spider bites>

While you can do everything in your power to avoid being bitten by a venomous spider, sometimes nature has a way of getting to us regardless. If you find that you are the victim of a spider bite, then try to remain calm and carry out the following actions:

  • For mild pain, take painkillers.
  • Wash the bite site using mild soap and warm water to reduce the chance of infection. You can also use antibiotic lotion.
  • If you have been bitten on the arm or leg, raise the limb.
  • Wrap an ice pack in cloth and hold this over the bite.
  • If bitten by a black widow spider and muscle cramps develop, head straight to the hospital for emergency treatment.
  • Where the person has difficulty breathing, convulsions, or becomes unconscious, you should call 911.
  • Try to collect the spider for assessment by your medical professional.
  • Never attempt to remove the venom by cutting the skin.
  • In some cases, you may require treatment using an antivenin.

Frequently Asked Questions

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