What does a brown recluse bite look like at first?

A red spot. That does not "go away" or respond to conservative treatment. Any non-healing skin wound may become suspect for a brown recluse bite, and these can progress to skin loss and scarring.
Red area. Red splotch or bump, usually very tender, not itching.
When I looked down. at my arm after clearing land - I saw a ring of white tissue surrounding a black spot. I was in the mountains alone. I began cutting away tissue every few hours - the tissue was white, necrotic, did not bleed and did not hurt to cut away. Boy, did that spider make me SICK!!!