In the Venezuelan coastal city of Maracaibo, they're known as piranhas. But these aren't the flesh-eating fish found in some South American rivers.
They're fast and ferocious thieves who residents say are increasingly attacking women.
The common denominator among the victims? All of them had long hair -- until thieves came at them with scissors, snipping it off.
"You have to see it to believe it," Maracaibo resident Egmari Villarreal said in a video posted on the Panorama newspaper's website. "We're not going to be able to have long hair anymore. As a woman, this is something traumatic."
Resident Sarai Madrid said she's seen it throughout the city.
"It's happening downtown, at the beach or at the mall, where you find a lot of young women," she told Panorama. "The thieves grab them by the hair, pull out some scissors and cut their hair. Then they sell it at beauty or hair salons."
Mariana Rodriguez told CNN affiliate Globovision that she was walking through a popular mall when she saw two women coming toward her.
"I thought they were going to steal my cell phone, because I had it in my hand at the time, but they took out scissors," she said. "They did not give me a chance to think or to run or anything. And when I looked, I no longer had any hair."
Maracaibo Mayor Eveling de Rosales told reporters that police were stepping up security to stop the attackers.
"As part of our operation of citizen security, we are giving them a forceful response, posting men and women to keep watch and stop this from continuing to happen," she said.
Jairo Ramirez, Zulia state's security secretary, told the newspaper that authorities have stepped up patrols after hearing about the reported thefts, but they haven't received any formal complaints.
"I do not know to what degree it is happening," he said. "I have not learned of any formal complaints of this type. I'm not saying it doesn't exist, but it is not very clear."
At least one such attack has also been reported in neighboring Colombia, CNN affiliate Caracol reported.
Arlen Luna told Caracol last year that she was wearing her hair in a braid when thieves attacked her in the Colombian city of Barranquilla.
By the time she realized what had happened, the thieves had already fled, and a chunk of her hair spanning about 20 centimeters (8 inches) was missing.
From the robber's perspective, it's quick and relatively easy money.
Hair stylist Israel Rodriguez told Caracol that synthetic hair costs anywhere from $40 to $160, depending on its quality. But natural hair can cost more than $500, he said.
All the more reason to guard your tresses.