One of the failed experiments for Umbrella, the Lurker is basically a frog infected with the T-virus. Like most infected animals, the frog grew in size and its senses and mobility increased. It would use its tongue became a weapon; the tongue had the ability to impale a human. Its digestive systems underwent drastic mutations as well; it became capable of swallowing a human whole.

The main problem with the Lurkers was their lack of intelligence. The Lurkers retained their frog like behavior, they could not be given orders, and they had no capacity to learn. Thus their use as a B.O.W. was gone, the experiments were cancelled but some remained alive and inhabited the waters near the Umbrella facilities.