How To Tell the Difference Between a Spider Bite and a Mosquito Bite

Reviewed on 3/23/2021

There are a few ways to determine whether you have a spider bite rather than a mosquito bite.
There are a few ways to determine whether you have a spider bite rather than a mosquito bite.

If you have an insect bite, you’ll often notice some redness and itching in the spot where you were bitten. If you’re not sure what kind of bug caused the bite, you may not know how to best treat the symptoms. There are some ways to tell the difference between a spider bite and mosquito bite and some clues for when you should seek medical care.

What is a spider bite?

Spiders are not technically insects. They are arachnids which are a class of arthropods that also includes scorpions, mites, and ticks. There are more than 45,000 known species of spiders around the globe and around 3,500 kinds in the United States. Around 50 of those have venom and can bite humans. Spiders have tiny fangs. When they bite, the fangs puncture your skin and inject venom. All of the symptoms related to spider bites are your body reacting to the venom.

The majority of spiders in the United States are not dangerous to humans. Spiders also not are usually aggressive. The majority of bites happen when the spider is trapped or accidentally contacted. 

Most spider bites cause minimal symptoms — like a red spot with some itchiness — and go away on their own within a week. There are a few kinds, however, that can be dangerous and require a doctor’s care. Venomous spiders in the United States include the black widow and brown recluse spiders. 

What is a mosquito bite? 

Mosquitoes, unlike spiders, are actual insects. They puncture your skin with their long funnel-like mouth to draw up blood. Your skin reacts with some redness, swelling, and itching in the spot where it is punctured. While the actual bites from mosquitoes are not dangerous, they can transmit lethal diseases like malaria, yellow fever, and dengue

There are a few ways to determine whether you have a spider bite rather than a mosquito bite. Generally speaking, mosquito bites cause some irritation and discomfort but resolve on their own within a couple of days. Rare instances of serious reactions have occurred, but they are very infrequent.

Symptoms of a mosquito bite include: 

  • A puffy, red bump appearing minutes after the bite
  • A firm, red or brown bump in the days following the bite 
  • Itching
  • Localized swelling

Any bite that does not begin to resolve itself or seems to be getting worse should be examined by your doctor.

Types of spider bites 

Non-dangerous spider bites

Most spider bites are irritating but not dangerous to humans. They usually last a day or two and are entirely resolved within a week. The symptoms of a non-dangerous spider bite include:

  • Redness at the spot of bite, typically smaller than a quarter
  • Swelling and tenderness
  • Itching
  • Pain that can feel similar to a bee sting

Brown recluse spider bite

The brown recluse spider (Loxosceles reclusa), also known as the “fiddle back spider” or the “violin spider” because of its markings, tends to live in undisturbed places like closets or attics. Bites can range from mild to serious. 

Symptoms of a brown recluse bite can include:

  • Redness followed by a blister at the site of bite
  • Mild to intense pain and itching for two to eight hours
  • An open sore with tissue breakdown developing a week or more after the bite
  • Fever and chills
  • Tiny, flat red and purple spots all over your body
  • Nausea and vomiting
  • Joint pain

Black widow spider bite

The black widow spider (Latrodectus mactans) is an all-black spider except for the red or orange hourglass marking on its abdomen. A shy spider, the black widow only bites when threatened. 

Many black widow bites cause only a moment of pain and some redness that resolves within a few days. However, some people may have a more severe reaction and require medical care. Symptoms of a black widow bite can include:

Diagnosis for spider bites

If possible, try and capture the spider that bit you. Bringing the actual spider will help your doctor quickly identify the type of spider it is and how to treat it.

Without the offending spider’s presence, your doctor will gather information about when and where you sustained the bite. Your doctor will also examine the bite to determine what the symptoms indicate.

Treatments for insect bites

Home care 

If you receive an insect bite — either a spider bite or mosquito bite — there are some ways to manage the irritation and discomfort at home:

If your bite symptoms do not go away within a few days, get worse, or are accompanied by fever, wheezing, or a body-wide rash, call your doctor.

Your doctor can use specific medication to counteract the effect of specific spider venom — black widow or brown recluse — and to ensure that you do not suffer any complications. This may include antibiotics to prevent a secondary infection. If you believe that one of these spiders is responsible for your bite, you should try to safely collect the spider and seek care right away.

Possible complications and side effects of insect bites

The vast majority of spider bites and mosquito bites cause minor irritation and go away within a few days. However, if you are bitten by a black widow or brown recluse spider, the complications can be serious. Untreated venomous spider bites can cause:

If you’re unsure whether you have a spider bite or mosquito bite, your doctor will be able to help you tell the difference.

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References
SOURCES:

American Academy of Allergy Asthma and Immunology: "Take a Bite Out of Mosquito Stings."

American Academy of Family Physicians: "Common Spider Bites."

American Osteopathic College of Dermatology: "Spider Bites."

Centers for Disease Control and Prevention: "Mosquito Bite Symptoms and Treatment."

Childrens MD: "Signs and Symptoms of a Brown Recluse Spider Bite."

Fairview: "Black Widow Spider Bite."

National Geographic: "Mosquitoes."

National Geographic: "Spiders."

The National Institute for Occupational Safety and Health: "Venomous Spiders."

Seattle Children’s Hospital: "Spider Bite."

Stanford Children’s Health: "Spider Bites."

UC Riverside Department of Entomology Spider Research: "Not Recluse."

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