Without seeing it, it sounds like a baby Brown Recluse spider. The wound certainly sounds like it. Brown Recluse bites are very serious.
My leg is still red but not as inflamed as it was so I might live. No heat coming off it today which is good. Alcohol, neosporin stuff and a vibrator to get the blood flowing around it twice a day. It was the teeniest little spider to cause such a reaction! Hubby had a brown recluse bite him a years ago which took forever to heal and the scar is still there.