UPPER DARBY POLICE were searching Wednesday for a 21-year-old woman who allegedly attacked her mother while she was bathing by biting her on the hand and both legs.

Part of the mother's thumb is missing, and she was in serious condition at the Hospital of the University of Pennsylvania.

"It's domestic cannibalism," said police Superintendent Michael Chitwood. "We never found the tip of the finger. We don't know whether she ate it or swallowed it. Totally out of control. We don't know if she was high on drugs or what."

Kirstie L. Foley, 21, who lives in an apartment with her mother on Marshall Road near Long Lane, is wanted for aggravated assault, simple assault and harassment.

Chitwood said it was unclear why Foley was arguing with her mother, who is believed to be 42 years old. The incident occurred over the weekend, but the woman remains in serious condition due to the number and severity of the bites.

"She almost took off the thumb," Chitwood said. "Nasty."

In 2009, an Upper Darby man almost chopped off his fiancée's middle finger, then bit her arm, because she didn't place the cheese on his meatball sandwich correctly.

Last month, a bite-fight was reported behind the Hannum's Harley Davidson shop in Chadds Ford. Police described it as a road-rage incident.