Spider bites can be mistaken for other skin sores that are red, painful or swollen. Many skin sores attributed to spider bites turn out to have been caused by bites from other bugs, such as ants, fleas, mites, mosquitoes and biting flies. Skin infections and other skin conditions, even burns, can be mistaken for spider bites.
Your doctor will likely diagnose a spider bite based on your history and your signs and symptoms. The process might involve determining whether anyone saw a spider bite you, having an expert identify the spider, and ruling out other possible causes of the signs and symptoms.
Black widow identification
Black widow spider
The black widow spider is known for the red hourglass marking on its belly.
Some clues for identifying black widow spiders include:
- Shiny black body with long legs
- Red hourglass shape on the belly
- Length of entire body, including legs, about 1 inch (2.5 cm) across
Brown recluse identification
Brown recluse spider
The brown recluse spider is known for the violin-shaped marking on its top.
Some clues for identifying brown recluse spiders include:
- Golden or dark brown body with long legs
- Dark violin shape on top of the leg attachment segment
- Six eyes — a pair in front and a pair on both sides — rather than the usual spider pattern of eight eyes in two rows of four
- Central body is about 1/2 inch (1.2 cm) across
Most spider bites usually heal on their own in about a week. A bite from a recluse spider takes longer to heal and sometimes leaves a scar.
First-aid treatment for spider bites includes the following steps:
- Clean the wound with mild soap and water. Apply an antibiotic ointment three times a day to help prevent infection.
- Apply a cool compress over the bite for 15 minutes each hour. Use a clean cloth dampened with water or filled with ice. This helps reduce pain and swelling.
- If possible, elevate the affected area.
- Take an over-the-counter pain reliever as needed.
- If the affected area is itchy, an antihistamine, such as diphenhydramine (Benadryl) or certirizine (Zyrtec), might help.
- Observe the bite for signs of worsening or infection. You might need antibiotics if the bite develops into an open wound or becomes infected.
For pain and muscle spasms, your doctor might prescribe pain medicine, muscle relaxants or both. You might also need a tetanus shot.
Black widow antivenom
If a black widow bite is causing severe pain or life-threatening symptoms, your doctor might recommend antivenom, which is usually given through a vein (intravenously). Symptoms usually ease within about 30 minutes of receiving the antivenom. Antivenom can cause serious allergic reactions, so it must be used with caution.
Preparing for your appointment
If you've been bitten by a spider that you suspect is dangerous, call your primary care doctor or go to an urgent care center. If your doctor has online services, an option may be to email a photo of the spider to your doctor.
What you can do
To help your doctor understand your symptoms and how they might relate to a spider bite:
- Bring the spider or a photo of the spider with you, if you can do so safely
- List any symptoms you're experiencing
- List questions to ask your doctor
Some basic questions you might want to ask include:
- Is this a dangerous spider bite?
- If this isn't a spider bite, what are possible causes for my symptoms?
- Do I need any tests?
- How long will my symptoms last?
- What is the best course of action?
What to expect from your doctor
Your doctor is likely to ask you a number of questions. Being ready to answer them might reserve time to go over any points you want to spend more time on. Your doctor might ask:
- When did you begin experiencing symptoms?
- What were you doing in the hours before your symptoms started?
- Have your symptoms gotten worse?
- Does anything relieve your symptoms or make them worse?