Most of the time, spider bites are not harmful, and spiders rarely bite unless they feel threatened.
You might not even notice the redness, pain, or swelling that comes from a spider bite. Redness, pain, and swelling are caused by numerous other skin wounds and bug bites. Therefore, it is difficult to be certain that your wound was caused by a spider unless you actually witnessed the bite.
Only a few species of spiders in the world possess venom and fangs long enough to penetrate human skin. There are about 30 species of widow spiders and more than 140 species of recluse spiders worldwide.
A spider bite typically presents as a red, inflamed, itchy, or painful bump on the skin, and it may even go unnoticed. Most of the time, harmless spider bites don't cause any other symptoms.
A bacterial infection, for instance, may be the cause of many skin sores that appear identical. Some spiders, like widow and recluse spiders, may cause serious symptoms when they bite.