Red Superfly
You creepy little stalker
Actually, we could say it was radioactive - it may have had radiation induced to the DNA to make it become the super-spider, who knows eh?
I just found it wierd that they took what was one of the most famous bits about Spiderman (everyone must know that he was bitten by a radioactive spider by now - everything from Dexters Lab to The Simpsons has made fun of it at one point or another) and changed it, for no good reason.
Every reason for changing it so far hasn't been good enough IMO.
The thing is, was that the Spider was a centerpiece for the experiment. They were testing on it, and had loads of them. They would have found out (and by the movies logic they could still) about it being able to grant its victim amazing spider powers eventually. In the comics there was no risk of that, because the spider died and the subject was closed, Peter, because of this, also had trouble removing his powers because it was such a "freak" occurence, and he got stuck with them.
In the movie, if he wants to remove his powers, he has plenty of research material to swipe due to them actually doing research and creating from scratch, these amazing spiders. The comic book was far more interesting because Peter had to try and unravel the mysteries of his superpowers himself, in order to understand them.
Plus, I just liked the whole idea of closure. I don't like the fact that Mary Jane could become Spider-Woman, or that a random-scientist could get bitten by the exact same spider. The spider is also portrayed as an aggressive SOB who just randomly bites people in the movie, whereas the comic book spider bit out of instinct from its fatal poisoning. This means, there's a good chance that those other fourteen spiders, along with the one that bit Peter and RAN AWAY (WTF?) would just randomly bite people, because they seem to do it for fun.
For the record, I, as a movie fan, would have no trouble understanding the fact that a radioactive spider (given special neogenic rays) would have the ability to pass on its powers before it died.