A spider bite looks like the bite of many other arthropods.  In some cases if you look closely you will see two tiny puncture wounds left by the spider's fangs.

The Average Spider Bite

Like most insect bites, the area affected will experience redness, slight swelling, and itchiness.  Then, depending on the venom injected, the local site may grow in size or the redness may expand even further.  Different people will react differently to spider bites depending on their sensitivity levels and the amount of venom that the spider injects. 

Do All Spiders Bite?

Spider bites are not common, as most spiders do not bite humans unless provoked.  Technically, all spiders bite and are venomous as this is their natural method of paralyzing and obtaining food.  Very few are harmful to humans as the spider's fangs are either not long enough or strong enough to penetrate the skin or the venom has no effect on the human body.

The two spider bites most harmful to man in North America are the Brown Recluse Spider bite and the Black Widow Spider bite.

Brown Recluse Bite

The bite of the Brown Recluse Spider injects venom that is a cytotoxin.  Cytotoxins cause necrosis, or deadening of the tissue.  The bite itself will blister, harden, and ultimately slough off, often leaving a volcanic-like scar.  Depending on the bite, this can cause serious damage and can result in death in those most vulnerable such as children and the elderly.

Black Widow Bite

If you look very closely, the Black Widow bite has two bright red puncture marks in the center.  The Black Widow injects venom that contains a neurotoxin.  Neurotoxins attack the nervous system.  There is an anti-toxin for the Black Widow bite.  These bites are generally not deadly but are more harmful to those most vulnerable.