How Long Does It Take For A Spider Bite To Show Up?
How to Know When a Spider Bites and What to Do About It
- 1 How to Know When a Spider Bites and What to Do About It
- 2 Identifying a Spider Bite: What Does One Look Like?
- 3 Spider Bites Usually Heal on Their Own. Here’s When to Seek Medical Attention
- 4 Why Do Spiders Bite People?
- 5 Spider Bite
- 6 Is this your child’s symptom?
- 7 When to Call for Spider Bite
- 8 Seattle Children’s Urgent Care Locations
- 9 Care Advice for Non-dangerous Spider Bites
- 10 Is It a Spider Bite? Probably Not
- 11 Spider Bites Rare
Medically Reviewed by Ross Radusky, MD
You spot an angry-looking red welt on your leg, and it seems too big to be a mosquito bite. Must be a spider bite, right?
Not so fast. “People wake up in the morning and find a red mark, and immediately call it a spider bite,” says Rick Vetter , a retired staff research associate and entomologist at the University of California, Riverside. But, he says, most of the skin issues people pin on spiders are actually other types of bug bites or skin issues.
Other researchers back Vetter up on this. “Spider bites are really rare,” says Jonathan Day, PhD , a professor of medical entomology at the University of Florida. He explains that most “spider bites” are more likely mosquito bites that were scratched and became infected. “Spider bite is a catchall grouping whenever there’s a severe skin infection; they’re all lumped in as spider bites,” he says.
So the first thing every spider expert in America would like people to know about spider bites is that they’re uncommon and often misdiagnosed. That said, some spiders do bite people, and the result can be ugly.
Identifying a Spider Bite: What Does One Look Like?
A lot of things. “There’s no one true spider bite,” Vetter says.
Spider Bites Can Look Very Different
Different types of spider bites may provoke different reactions in different people, he says. Even if you’re talking about just one type of spider — say, the brown recluse — its bite could cause a range of reactions: “everything from a little pimplelike bump to a rotting-flesh lesion,” he says.
At the same time, Vetter allows that different types of spider bites do produce distinct reactions. “I’ve had patients contact me saying, ‘This mark on my leg was either from a widow or a recluse,’ but that’s like saying you either got stabbed or trampled to death,” he says. His point: Black widow and brown recluse bites are so different that they could never be mistaken for one another.
But when it comes to common household spiders, hobo spiders, and other domestic varieties, a spider’s bite has some predictable characteristics.
How to Identify Which Spider Bit You
Broadly speaking, a spider’s bite tends to resemble a bee sting: a sharp prick of pain is followed by a red, inflamed skin lump that may hurt or itch but that goes away after a few days. (1) But when it comes to venomous spider bites, there are characteristic signs and symptoms.
Brown recluse bites sting, and they can resemble anything from small blisters to large, rotting-flesh sores, Vetter says. “Its bite causes the collapse of the capillary bed”— also known as skin necrosis (2) — «so people who are obese and have poor support of the capillary cells may have a more massive reaction,” he explains. Along with a wide variety of skin symptoms, brown recluse bites can cause chills, fever, nausea, and other flu-like symptoms common to infections. (3) The brown recluse’s bite is poisonous and can result in coma, kidney failure, or even death.
Because of the severe reaction a brown recluse bite can trigger, these spiders are likely blamed for more harm than they actually cause. The reality is that the brown recluse spider is limited in its geographic range: It’s found in the central and southern United States. (4) The Centers for Disease Control and Prevention (CDC) notes that while venomous spiders are dangerous, they aren’t usually aggressive. (2)
Black widow bites can in some cases cause skin lesions, ranging from small red marks to angry, red, streaky skin patches that are inflamed or contain pus. “But most of the reaction will be on the inside,” Vetter says.
Black widow bites contain potentially deadly amounts of venom and tend to be painful right away. Although that pain starts around the bite site, within an hour, it often spreads to the chest or abdomen, depending on whether the bite occurred on the victim’s upper or lower body. Other symptoms can include everything from headaches, muscle weakness, and difficulty breathing, to seizures, numbness, and painful muscle cramps. (5)
Hobo spiders, wolf spiders, house spiders, and the bites of other domestic types do not contain venoms that are of medical importance to humans, Vetter says. They can bite, he adds. But the result is likely to be similar to a bee sting — meaning a sharp pain, followed by a swollen, red, painful lump at the bite site.
Spider Bites Usually Heal on Their Own. Here’s When to Seek Medical Attention
If you think you were bitten by a black widow or brown recluse spider — either because you actually felt and saw the spider, or you’re experiencing the types of skin or systemic symptoms consistent with their bites — head to the emergency room. (6) Vetter says that recluse bites do usually heal on their own and don’t cause scarring wounds. But it’s better to play it safe.
If your spider bite isn’t causing any internal symptoms, or you’re sure it wasn’t a black widow or brown recluse that bit you, follow these steps:
- Clean the bite with soap and water.
- Swab the bite with alcohol to prevent an infection, Dr. Day recommends.
- Apply ice or a cold compress to keep the swelling down.
If pain or itching develops at the bite site, it’s fine to take OTC pain meds or antihistamines for relief. But if pain spreads beyond the site of the bite, or if the swelling, inflammation, or redness are getting worse even a day or two after the bite occurred, get medical attention. You may have a secondary infection — something caused by bacteria getting into the bite — or you may have been bitten by a widow or recluse, Day says.
Why Do Spiders Bite People?
Unlike many other biting bugs, spiders are neither bloodsuckers nor flesh eaters. Vetter says they bite people for one reason only: self-defense.
“Biting is a last-ditch defensive response if a spider is being squashed,” he says. This can happen when someone rolls over in bed on top of a spider — or sits down on one, he says. “I’ve transferred spiders hundreds of times, and they’ll be running all over my arm and have no interest in biting,” he adds.
So while spider bites do occur, they’re far less common than most people assume.
Is this your child’s symptom?
- Bite from a spider
Symptoms of a Spider Bite
- Most spider bites cause local pain, redness and swelling. It’s much like a bee sting reaction.
- A few spiders (such as the Black Widow) can cause a more severe reaction.
- Helpful if spider seen on the skin or around the child
Cause of Spider Bite Reactions
- Most spiders have tiny fangs. They inject venom into the skin.
- The venom is what causes all the symptoms.
Types of Spider Bites
Black Widow Spider Bite
- A shiny, jet-black spider with long legs (total size 1 inch or 25 mm).
- A red (or orange) hourglass-shaped marking on its under-side.
- Causes immediate local pain and swelling.
- Sometimes, you can see 2 fang marks at the bite site.
- Severe muscle cramps (especially stomach cramps) occur within 1 to 6 hours. These last 24 to 48 hours.
- Rarely causes death. Exception: bitten by several spiders or small child is bitten.
- Note: many are dry bites because the fangs are small.
- The brown widow spider is related to the black widow. It is found in southern US.
- Brown widow spider bites are treated the same as black widow bites.
Brown Recluse Spider Bite
- A brown spider with long legs (total size ½ inch or 12 mm).
- A dark violin shaped marking on top of its head.
- Causes pain at the bite. Blisters form within 4 to 8 hours.
- The center becomes bluish and depressed (crater-like) over 2 to 3 days.
- Skin damage may require skin grafting in 10% of cases.
- Other symptoms such as fever, vomiting, muscle pain can occur. No life-threatening symptoms occur.
- Brown recluse spiders are hard to identify. If you can, bring the spider along in a jar.
Non-dangerous Spider Bites
- More than 50 spiders in the U.S. have venom. Their bites cause reactions that are not serious. This includes pain or redness at the bite site.
- The bites are painful and swollen. This lasts for 1 or 2 days. They can feel and look like a bee sting.
- Some single, unexplained, tender bites that occur during the night are due to spiders.
When to Call for Spider Bite
Call 911 Now
- Trouble breathing or wheezing
- Passed out (fainted) or too weak to stand
- You think your child has a life-threatening emergency
Call Doctor or Seek Care Now
- Fever and bite looks infected (spreading redness)
- Your child looks or acts very sick
- You think your child needs to be seen, and the problem is urgent
Contact Doctor Within 24 Hours
- New redness starts more than 24 hours after the bite. Note: any redness in the first 24 hours is due to venom.
- More than 48 hours since the bite and redness now getting larger
- Bite starts to look bad (such as skin damage, blister or purple color)
- Bite pain lasts more than 2 days
- You think your child needs to be seen, but the problem is not urgent
Contact Doctor During Office Hours
- You have other questions or concerns
Self Care at Home
- Non-serious spider bite
Seattle Children’s Urgent Care Locations
If your child’s illness or injury is life-threatening, call 911.
- Federal Way
Care Advice for Non-dangerous Spider Bites
- What You Should Know About Spider Bites:
- Most spider bites look and feel like a bee sting.
- The main symptoms are pain and redness.
- Here is some care advice that should help.
- Clean the Bite:
- Wash the bite well with soap and water.
- Cold Pack for Pain:
- For pain or swelling, use a cold pack. You can also use ice wrapped in a wet cloth.
- Put it on the bite for 20 minutes.
- Pain Medicine:
- To help with the pain, give an acetaminophen product (such as Tylenol).
- Another choice is an ibuprofen product (such as Advil).
- Use as needed.
- What to Expect:
- The swelling and pain lasts for 1 to 2 days.
- It should not be any worse than a bee sting.
- Call Your Doctor If:
- Severe bite pain lasts more than 2 hours after pain medicine
- Stomach pains or muscle cramps occur
- Bite pain lasts more than 2 days (48 hours)
- Bite starts to look infected
- You think your child needs to be seen
- Your child becomes worse
And remember, contact your doctor if your child develops any of the ‘Call Your Doctor’ symptoms.
Disclaimer: this health information is for educational purposes only. You, the reader, assume full responsibility for how you choose to use it.
Last Reviewed: 06/09/2020
Last Revised: 03/21/2020
Copyright 2000-2020 Schmitt Pediatric Guidelines LLC.
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Is It a Spider Bite? Probably Not
Researchers Say Spider Bites Are Overdiagnosed, yet Underappreciated
July 13, 2011 — Spider bites aren’t as common as most people and most doctors think, according to a new analysis.
At the same time, researchers also say poor understanding of truly dangerous spider bites delays treatment when a person really has been bitten by a dangerous spider.
For example, the bite of the brown recluse spider can cause death of a sizeable area of skin (skin necrosis) resulting in a deep, scarring ulcer. Yet even in areas infested with brown recluse spiders, true bites are uncommon.
The analysis is published in the July 14 online issue of The Lancet.
«The treatment of patients with suspected spider bite is not straightforward because of overdiagnosis of skin necrosis as being attributable to spider bites while, at the same time, serious [spider bites] . are not being recognized and treatment is delayed,» write Geoffrey Isbister, MD, of the University of Newcastle, Australia, and Hui Wen Fan, PhD, of Butantan Institute, Sao Paulo, Brazil.
Isbister and Fan note that there are more than 41,000 known species of spider, but that very few have bites harmful to humans.
The names of the two U.S. spiders with harmful bites are well known: the black widow and the brown recluse. The two spiders have different venoms:
- The bite of the black widow may not be very painful at first. Pain onset usually is gradual and usually takes the form of back and belly pain that can last for hours or even days.
- The bite of the brown recluse (and 12 other recluse spiders in North America) can be mild and just cause a mild, itchy bump. But in severe cases, the bite may be painless at first, but over the next two to eight hours develop a sharp, deep pain followed by a burning feeling. The area around the bite reddens and spreads into a deep ulcer that can be as wide as 16 inches across and can take six to eight weeks to heal.
What about other spiders?
«Many additional spiders . have been implicated,» wrote Mayo Clinic dermatologist David L. Swanson, MD, and University of California spider expert Richard S. Vetter, MS, in a 2006 report. «Unfortunately, most of the implicated spiders have been falsely elevated to a status of medical significance through circumstantial implication and repetitive citation in the medical literature.»
Spider Bites Rare
Because of the range of symptoms, people often mistake insect bites, chemical burns, allergic reactions, and skin infections for spider bites. But true spider bites are relatively rare, even in households found to be infested with hundreds of brown recluse spiders.
Unless the brown recluse spider is caught in the act, doctors must be willing to challenge the diagnosis of brown recluse spider bite, Swanson and Vetter note.
It’s a different story in South America, where recluse spider bites are a major health problem. But in the U.S., the spider’s range is from the southern Midwest to the Gulf of Mexico. They’ve been found from southeastern Nebraska through southern Iowa, Illinois, and Indiana to southwestern Ohio, extending south from northwestern Georgia to central Texas. Unless transported, they are not found west of the Rockies.
Extensive searches turn up no brown recluse spiders in the southern third of Georgia and in Florida. But that doesn’t stop people from thinking they’ve been bitten by a brown recluse. No recluse species are native to Florida, yet over a six-year period Florida poison control centers received 844 brown recluse bite reports — 15% of them from medical personnel.
In Georgia, researchers asked people to send them their brown recluse spiders. Some 1,060 people sent in spiders they believed to be brown recluses. Only 19 really were. Most turned out to be harmless Southern house spiders, wolf spiders, or orb weavers. The experts who conducted the study went on a field trip to seek out brown recluse spiders in Georgia; they found none. Yet over that period there were hundreds of reported brown recluse bites.
Brown recluse spiders are not rare in many areas of the U.S. In a 2009 report, Vetter and colleagues noted that a family in Lenexa, Kan., collected 2,055 brown recluse spiders over six months in their home. In an Oklahoma barn, spider hunters found 1,150 brown recluses in just three nights.
Even though the brown recluse is a common house spider in several states, bites are relatively uncommon. For example, the four family members in the Lenexa, Kan., house suffered no bites after eight years in the house.
It’s lucky spider bites are rare, as there’s no definitively proven treatment. While anti-venom exists, there’s no proof it helps — although there’s a long history of safe use, so Isbister and Fan recommend continuing to use it. However, anti-venom probably does not prevent the ulceration and scarring of a severe brown recluse bite.
«Studies are needed to prevent the unnecessary use of ineffective antivenom, which puts patients at risk of allergic reactions,» they suggest.
Isbister, G. and Fan, H.W. The Lancet, published online July 14, 2011.
Vetter, R.S. Journal of Medical Entomology, January 2009; vol 46: pp 15-20.
Swanson, D.L. and Vetter, R.S. Clinics in Dermatology, 2006; vol 24: pp 213-221.
University of California, Riverside Spiders Site.
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