Spider bites are often blamed for marks they didn't cause — but a small number of spiders can cause real harm. Here's how to tell a routine bite from one that needs attention.
“Spider bite” is one of the most over-diagnosed skin marks. Many bites blamed on spiders are actually from other insects, or are skin infections. That said, a few spiders — such as widow and recluse species in some regions — can cause reactions that need medical care. Knowing the difference helps you stay calm and act appropriately.
What most spider bites look like
A typical spider bite resembles other bug bites: a red, swollen, sometimes itchy or tender bump, occasionally with two tiny puncture marks. Most cause mild local symptoms that improve within a few days with basic care — cleaning the area, a cool compress, and keeping it from getting infected.
Signs a spider bite needs attention
A minority of bites progress differently. Watch for:
- Severe or worsening pain spreading from the bite over hours.
- A blister or a darkening, ulcerating wound at the bite site.
- Muscle cramps, abdominal pain, sweating, nausea, or fever.
- Any sign of a severe allergic reaction — trouble breathing, facial or throat swelling, or feeling faint.
What to do
- Wash the bite with soap and water and apply a cool compress.
- Keep the affected limb elevated and avoid scratching.
- Take note of when it happened and photograph how it changes over time.
- If you can safely identify the spider, that information can help a clinician — but never put yourself at risk to do so.
When to see a doctor
Seek medical care if pain is severe or spreading, if the wound blisters or ulcerates, if you develop body-wide symptoms such as cramps or fever, or if you suspect a bite from a widow or recluse spider. For any breathing difficulty or facial swelling, call your local emergency number immediately.
FAQ
Are two puncture marks proof of a spider bite?
Not reliably. Two marks can suggest a spider, but many bites and skin problems mimic this. Symptoms and how the bite evolves matter more than appearance alone.
How do I know if it's serious?
Severe spreading pain, an ulcerating wound, body-wide symptoms, or any allergic reaction are reasons to seek medical care promptly.
