I have a hard painful lump on my spider veins and hot to the touch why is this?

Clotted spider vein: There is most likely a clot in the superficial vein. If you are at risk for blood clotting (pregnant, on birth control pills, recent flight, cancer patient, immobilized, hypercoagulability disorder, previous history of blood clots, history of trauma), you should see you doctor to make sure you do not have a deep vein thrombosis. Otherwise, warm soaks will help the thrombophlebitis resolve.

Probably phlebitis: I agree with drs. Vaniver and rosenfeld, you should have this evaluated by a physician. Although it is most likely to be phlebitis rather than a blood clot or an infection, phlebitis of a spider vein is unusual. The phlebitis is probably in a vein underneath your spider veins. This should be looked at with ultrasound. Ice and/or moist heat and anti-inflammatory meds can make things feel better.