Tokyo - A Japanese zoo is trying to do the impossible - improve the image of cockroaches, putting on an exhibition of one of the world's most hated insects.With a whopping - and disgusting – 4 000 species around the planet, the hardy creature can survive almost anywhere, but is most commonly encountered by city-dwellers in grubby corners of the kitchen, or roaming around the floor at night.Staff at Shunanshi Tokuyama Zoo in Yamaguchi, western Japan, say the cockroach gets a bad press, and actually performs a vital job."They have such a negative image," a zoo spokesperson told AFP. "But they're actually playing an important role in the food chain."Worrying speedy bugsImportant, but not very pleasant-sounding: eating rotting carcasses and dead plants on forest floors.One highlight of the exhibition will be a five-way race among cockroaches, where visitors can watch the worryingly speedy bugs whizz down a track.If that's not entertainment enough - hard to credit - the zoo is offering the chance to get your hands on a Madagascar Hissing Cockroach, which can grow as long as 7cm.No need to worry about this, though, assures the zoo - Madagascar Hissing Cockroaches can't fly. But they can hiss.The exhibition has around 200 creatures from a total of 15 species on display, and is already proving popular, the spokesperson said, adding 70% to 80% of visitors are stopping by.