Using a gland from vampire bats, Dr. Kirk Langstrom created a serum that could restore a deaf person's hearing. But when Langstrom tested the concoction, he noticed it had the slight side effect of turning him into a blood-sucking bat monster.
Because he can turn people into a creature like himself by sucking their blood, it's easy to see why Man-Bat is one of the most terrifying people in Gotham.
However, Langstrom would probably be the easiest Batman foe for Spider-Man to defeat. Due to his hypersensitive hearing, Man-Bat is vulnerable to sonic attacks. Because Spidey has a plethora of sonic weapons thanks to his encounters with Venom and Carnage, fighting Langstrom wouldn't prove a challenge.
Now, let's look at the worst case scenario. What if Man-Bat gets the drop on Spider-Man and bites him, turning him into a bloodsucker like himself?
If this happens, ol' Web-head has nothing to worry about. As has been explained in 2006's Blade #1, Spider-Man's radioactive blood will kill any infection, including a vampiric one. In fact, Spider-Man should let Man-Bat bite him, since his infected blood would cause the supervillain to pass out from radiation poisoning.