What spider bite hurts the most?

Black widow: Black widows (latrodectus species) are the most painful in the U.S. Though i'm not sure about other parts of the world. Latrotoxin can cause pain, sweating, rapid heartbeat and cramps, and other symptoms. Black widow bites can rarely be fatal. Most bites are not severe, but some are. Brown recluse bites usually cause local tissue problems. Any bite with symptoms should be seen by the doc.