The spider bite was apparently a lie on the singer's part, considering also what certain experts stated about that.
For example, entomologist Rick Vetter (at the University of California) stated back then:
"The fact that Michael Jackson says he has a spider bite is a bunch of crap … [Michael] Jackson has no idea what he's talking about" (Rick Vetter)
Rick Vetter also noted that spiders rarely bite people.
Also, video producer Marc Schaffel revealed that the wound was not by a spider bite, but by a self inflicted heroin needle:
"[Michael Jackson] had the IV (intravenous) stuff back then. It wasn't a spider bite. It was an IV he pulled out of his leg. The needle broke off" (Marc Schaffel, The Globe Interview)
Marc Schaffel was very close to Michael Jackson at that time.