While this is a list of the most venomous spiders, it’s essential to understand you should seek medical attention for any spider bite if you are allergic or experience symptoms that exceed those expected.
An allergic reaction to any spider bite could cause anaphylaxis. While it is rare, an anaphylactic shock could occur in some humans. Get immediate medical attention if you are bitten by any spider and experience rapid swelling of your throat, lips, tongue, or around your eyes. In the United States, use the 911 emergency system.
Anaphylactic shock is potentially fatal. Do not delay; get medical help immediately.
Related: The biggest spiders in the world.
The most venomous spider: Brazilian wandering spider.
It is the “wandering” nature of the Brazilian wandering spider that makes it so dangerous to humans.
Most venomous spiders strictly use their venom to kill prey. Venom is a limited (if replenishable) resource needed for food consumption.
Spiders have adapted their defensive bites to drive off an attacker using injury and pain while conserving their venom for later use on smaller prey.
Therefore, most defensive bites delivered to large mammals (like humans) are considered to be “dry” and do not contain venom.
The Brazilian wandering spider’s habit of seeking shelter during the day under logs and blankets, in boots and inside clothing, or amongst banana plants often leads to accidental envenomation of humans. It is these venomous bites that dangerous to humans.
The effects of Brazilian wandering spider poison.
The effects of a venomous note from a Brazilian wandering spider on a human include:
- Severe radiating pain that quickly spreads throughout the effected limb.
- Visual hallucinations.
- Increased blood pressure.
- Breathing difficulties.
- Death by respiratory failure.
Most symptoms onset within 30 minutes of the bite and death for those untreated by anti venom can occur within 2-6 hours.
Noted without comment, some human male’s suffer long painful erections as a result of being bitten by Brazilian wandering spiders. So, of course, the venom is being studied as a treatment for erectile dysfunction.
Most venomous spider the Black widow spider.
Black widow spiders have a latrotoxin in their venom. The latrotoxin causes toxic effects in the vertebrate central nervous system “by depolarizing neurons, by increasing [Ca2+] i and by stimulating uncontrolled exocytosis of neurotransmitters from nerve terminals.”
Indeed, black widow spider bites can be dangerous and may result in severe muscle pain, abdominal cramps, abnormal sweating, high heartbeat rates, and muscle spasms. These symptoms persist for at least a week but may last for several weeks.
In the United States, each year, about 2,200 people report being bitten by a black widow. Still, no deaths due to black widows have been reported to the American Association of Poison Control Centers since 1983.
Even though black widow spiders are not aggressive and rarely bite humans unless startled or otherwise threatened, their venom is nearly 15 times stronger than a rattlesnake’s. It can cause muscle aches, nausea, and paralysis of the diaphragm, which can make breathing difficult, which, to small children, the elderly, or the weak, may be fatal.
What does a black widow spider bite feel like?
Black windows spider bites can cause pain that peaks within about three hours. This pain is accompanied by nausea, sweating, a spike in blood pressure, and fever.
If a black widow spider bites you, or you live where a black widow spider might bite your children, make sure everyone bitten gets prompt medical treatment.
Treatment for a black widow spider bite is best facilitated by killing and preserving the spider if possible. Indeed, don’t smash the spider to the point it is unrecognizable.
A doctor able to correctly identify the bite of a black widow spider will provide medications and an anti-venom that will relax your muscles and reduce your pain. The anti-venom will also counteract the venom injected by the spider.
Most venomous spiders: Brown recluse spiders.
You must stick your hand in a brown recluse spider web or seriously disturb one to receive a bite.
However, accidents do happen. For example, if a brown recluse spider bites you, you can expect the pain to range from mild to severe after a few hours.
Less than 10% of bites from brown recluse spiders cause any real tissue damage (there is no anti-venom available yet), but most bites heal and do not leave scars—even if medical attention is not sought.
Of course, everyone reacts differently to spider bites, so treat with first aid, collect the spider if possible, and seek immediate medical attention.
Signs and symptoms of Brown recluse spider poison.
Recluse spider bites can take a terrible course if left untreated. Initially, there is an eight-hour period of increasing pain at the bite site. Body aches, fever, and chills follow this.
Untreated, the center of the brown recluse bite wound can become pale and turn dark purple with a red ring around it. Worse, the wound can become an open sore with dying skin.
Brown widow spider poison: Effects and symptoms.
False black widows symptoms are often similar to, but much less severe, than those of an actual black widow bite.
According to this study: Black and brown widow spider bites in South Africa.
“The bite of the brown widow spider usually causes a mild form of envenomation characterised chiefly by local symptoms and signs. Most adult patients complain of a local burning sensation which often spreads to the regional lymph nodes.
Paraesthesiae in the surrounding skin and stiffness of the local muscles are often described. In a small percentage of patients abdominal and general muscular pain, as well as weakness in the legs, are experienced. On examination the bite site can usually be identified. It often manifests as a red macular spot or centrally blanched area surrounded by a 2 – 3 cm eryiliematous reaction.
Occasionally there is localised increase in sweat secretion in the form of small droplets. A low-grade raised temperature is sometimes noted. The condition is self-limiting and usually clears up within 1 – 2 days, although some patients may experience a feeling of local discomfort for an extended period.
Children may present with hyperactivity or restlessness and are more inclined to develop symptoms and signs of systemic envenomation.”
Are six-eyed sand spiders poisonous?
The six-eyed sand spider produces more toxic venom than any other spider. This venom can kill a rabbit. But can it cause a medically significant wound to a human?
Potentially. Six-eyed sand spiders have bitten so few people that little research, medical case studies, or word-of-mouth examples are available. Also, there is no anti-venom available as of today.
The threat, therefore, is the possible damage and destruction of red blood cells and the release of a strong hemolytic into the wound site. Researchers worry a six-eyed sand spider bite could produce blood vessel damage, bleeding, tissue destruction, and the death of affected tissue.
One last note, and one that further reduces the likelihood of the bite of a six-eyed sand spider as being dangerous—not every bite will contain venom or a large amount, if it anyway.
Most venomous spiders: Sydney Funnel-web.
The Sydney funnel-web spider (Atrax robustus) is a venomous spider native to eastern Australia, usually found within a 50-mile radius of Sydney. It is a member of a group of 40 species of funnel-web spiders known as Australian funnel-web spiders. Its bite is capable of causing severe illness or death in humans if left untreated.
The Sydney funnel-web has a body size ranging from 1/2 to 2 inches in length. These spiders are glossy and darkly colored, ranging from bluish-black, black, brown, or plum-colored hues.
The Sydney funnel-web spider poison is dangerous.
The Sydney funnel-web spider will let you know when threatened or provoked by rearing up on its back legs and displaying its fangs. If it must defend itself by biting, the Sydney funnel-web spider will retain a grip on you and keep biting.
Since 1981 antivenom has been available to treat victims, but treatment must be immediately sought as envenomation can begin within 30 minutes. In addition, small children suspected of being bitten must receive immediate medical treatment as death can occur within 15 minutes without it.
Symptoms of Sydney funnel-web envenomation include: “Facial paresthesias, nausea, vomiting, profuse diaphoresis, drooling, and shortness of breath. In addition, patients may become agitated, confused, and ultimately comatose.
“This is associated with hypertension, metabolic acidosis, dilated pupils, muscle twitching, and pulmonary and cerebral edema. Death results from pulmonary edema or progression to hypotension and circulatory collapse.”
Redback Spiders: Not the most venomous spiders, but a frequent biters.
Australia’s Redback spiders (Latrodectus hasselti) look like North America’s Black widow spiders (Latrodectusmactans). Indeed, these spiders are called redback black widow spiders, but it is a distinct species and only native to Australia.
Redback spiders are found throughout Australia and are common in urban settings and areas where construction and human activities have removed topsoil and vegetation.
During the summer, redback spiders are responsible for hundreds of bites of humans.
Redback spider bites.
Redback spiders frequently bite humans during the summer. Of the sexes, only the female’s bite is dangerous, and with an anti-venom available for decades, death is unlikely.
Since female redback spiders rarely leave their webs, most bites occur when humans place their hands in the webs and threaten the spider.
Redback spider bites cause extreme pain, muscle weakness, vomiting, nausea, and sweating 9especially at the site of the wound).
Administer first aid. Apply a cold compress to the bite location, collect the spider in a clear container if possible (to facilitate identification and treatment), and get medical attention.
How to prevent redback spider bites.
- Many redback spider bites are on the humans buttocks. So keep your outdoor furniture clean.
- Locate and destroy redback spider webs.
- Smash any egg sacs you find.
- Keep clothing and boots off the ground and check all apparel before putting it on.
- Keep your yard well-maintained.
Most venomous spiders: Wolf spiders.
Like the hobo spider, the wolf spider was thought to have had a dangerous bite for many years. However, the venom of a wolf spider is not a serious medical problem for most people. Indeed, these spiders have bites that produce only slight redness and swelling.
However, the lack of a venomous bite should not lead you to believe they are safe to pick up or mishandle. The wolf spider will bite if threatened, and that bite is painful enough to serve as a reminder to leave future wolf spiders alone.
Now, if you are reading this because a brown spider bit you, I have one caution. While a simple wash and treat with first aid might be all you need for a wolf spider bite, that does not mean it was the spider that bit you.
If you cannot positively identify that the bite came from a wolf spider, recover the (dead) spider and consult with a doctor. The doctor can use the dead spider (please don’t use enough for killing for the corpse to be classified as “remains unviewable”) to identify the spider for you.
Why speak with a doctor and bring the dead spider? A giant brown recluse spider looks a hell of a lot like a brown wolf spider. If you are bit by a brown recluse spider, you should get prompt medical treatment.
So, unsure which spider bit you? Then if it can be easily captured or killed, place it in a clear, tightly closed container so it may be identified—and get thee to a physician.
Yellow sac spiders: Not the most venomous spiders.
Both species of Yellow sac spiders in the United States are about the same size (females reaching up to .4 inches in body length and males .3 inches).
Cheiracanthium inclusum is cream or light yellow, with a dark brown mouth and palps. Cheiracanthium mildei has a yellow head and thorax and green abdomen. In addition, both spiders have darker “heart marks” or dorsal stripes running lengthwise down their stomachs. These markings often cause the spider to be mistaken for a Brown recluse spider.
The yellow sac spider’s eight eyes are nearly equal to the same size and are arranged in two slightly curved lines. This spider species also has two front legs that are much longer and less muscular than their other six legs.
Are Yellow sac spider bites dangerous?
The bite of a Yellow sac spider is painful and comparable to that of a wasp sting. If you are not allergic and can positively identify the source of the injury as that of the Yellow sac spider, it is not a medically significant wound.
You can expect the pain to last for a few hours and some swelling. Use proper first aid for a spider bite to treat the wound and prevent infection.
Is the bite of a Red widow spider poisonous?
Red Widow Spiders (Latrodectus bishopi) are endemic to Florida but only live in a restricted range. Currently, Red Widow Spiders dwell in Lake Wales Ridge and other Southern and Central Florida areas.
According to Hollenbeck, Jeff. “Species Latrodectus bishopi – Red Widow.” BugGuide. Iowa State University. Retrieved 20 September 2018.
“This spider is venomous and can be harmful to people. The female’s venom is a neurotoxin that causes sustained muscle spasm rather than local tissue injury.
Note from J. Hollenbeck:
A clear lymph fluid also oozes from the pores surrounding the bite. The muscle spasms are permanent, (at least my case) reoccurring several times a year for several minutes at a time. The bite was treated as L. mactans, although treatment may have been unnecessary, as spasms, oozing, and localized redness were the only effects of the bite.
Males and immatures do not bite.”
Contact between human red widow spiders is rare, due to their restrictive habitat.
How to tell if it isn’t one of the most venomous spiders.
Ruling out the bite of recluse spider is critical to determining if a nite is potentially medically significant. The mnemonic NOTRECLUSE by the UC DEPARTMENT OF ENTOMOLOGY states:
“N – numerous: Most recluse bites (and spider bites in general) are singular wounds where the spider will bite when being near fatality crushed between skin and some other surface. If there are multiple lesions, consider bacterial infections, shingles, pyoderma gangrenosum, bites by blood-feeding arthropods (fleas, mites, bedbugs), poison ivy, poison oak.
O – occurrence: Many bites occur when a sleeping person rolls over on a spider in bed or when dressing in the morning, putting on shoes or clothes that sat out on the floor overnight. Also, bites may occur when disturbing possessions in the attic, garage or basement. Recluses do not live in green vegetation so skin lesions that show up after gardening might be a plant-related fungal infection called sporotrichosis especially if lesions show up on the forearms and backs of the hands.
T – timing: Most recluse bites occur from April to September in the Northern hemisphere. Even in heated homes, recluses disappear for the winter. Skin lesions appearing during October to March “down time” are unlikely to be recluse bites. Exception: recluses might be disturbed when unpacking year-end holiday decorations taken out of storage.
R – red center: Except for mild envenomations, recluse bites are not red in the center of the lesion. Recluse venom destroys the capillary network at the bite site so red blood cells can’t get to the area. The more dynamic bites will be white, blue or purple at the bite site. If there is a red center, the differential diagnoses include streptococcal cellulitis or an arthropod bite or sting.
E – elevated: Recluse bites are flat or slightly sunken. If a lesion is raised up more than 1 cm above the normal skin surface, recluse bite is unlikely. Differential diagnoses include bacterial infection such as MRSA (methicillin-resistant Staphylococcus aureus).
C – chronic: Most recluse bites are healed by the third month. Differential diagnoses for longer lasting lesions include: pyoderma gangrenosum, non-melanoma skin cancer, tularemia.
L – large: Most recluse bites do not become larger than 10 cm (2 1/2 inches). Larger lesions might be pyoderma gangrenosum.
U – ulcerates too early: Recluse envenomations don’t usually ulcerate until day 7 to day 14. Earlier ulceration might be pyoderma gangrenosum or the very rare anthrax infection.
S – swelling: Recluse bites typically do not involve much swelling below the neck or above the ankles. However, bites above the neck can involve significant swelling, which can compromise breathing passages. Major swelling from below the neck to ankles indicates streptococcal cellulitis, bacterial infection or bee/wasp/ant bite/sting.
E – exudative: This may be the most important sign indicating that it is not a recluse bite: exudative. Recluse bites may form a small fluid-filled blister at the bite site soon after the bite but, in general, recluse bites are usually dry. If a skin lesion is exuding pus, blood or serum that indicates something other than spiders is the cause. One of the most common conditions mistaken for spider bite by the general public is a bacterial infection. The resistant MRSA is very common in human populations worldwide. A deep, weeping wound, especially on the lower leg might be pyoderma gangrenosum.”