A full facial view of any spider will leave the observer in little doubt of its killing ability. Two bulbous and powerful jaws, known as the chelicerae, protrude down from under the front margin of the carapace. Each chelicera bears a hinged fang that folds into a groove where there may be a number of cheliceral teeth against which to secure their prey. Both fangs have a single small aperture near the tip from which fine ducts lead up to the venom glands within the head.

Spiders fall into two groups, each being classified upon how they strike their prey. The fangs of Tarantulas are so hinged that they articulate in a front-to-back motion allowing them to strike their prey from above. Most other spiders have fangs that are hinged laterally, providing a left-to-right strike.