Reports of these 'sperm hunters' first surfaced in Zimbabwe's press in 2009, but police have so far only managed to arrest three women, who were found with a plastic bag filled with 31 used condoms.

The media has run reports of male hitchhikers being drugged at gun or knifepoint - and even with a live snake in one case.

The victims are then reportedly given a sexual stimulant and are forced into repeated intercourse, before being dumped by the side of the road.

The exact use of the sperm is unclear, but it is believed that it could be intended for traditional rituals that bring good luck.

National police spokesman Wayne Bvudzijena said: "We do not have the exact number of confirmed cases.

"These cases occurred mostly when the victims were hitchhiking and boarded private vehicles. We encourage people to use public transport."

Sociologist Watch Ruparanganda, of the University of Zimbabwe, commented that research for his doctoral thesis suggested that "there's some big racket somewhere, some big guys driving everything, but they are in the background and using these ladies".