If the plausible-sounding Book of Genesis is to be believed when it says that breeding pairs of every species were ushered aboard the Ark then it was a very cockroach-rich vessel indeed. Quite apart from all the cockroaches of the wider world there were at least 1100 (550 breeding pairs) of species unique to Australia on board. How they must have made Mrs Noah shudder! Two of those that swaggered aboard must have been a male and female of the Giant Queensland Burrowing Cockroach (pictured) Macropanesthia rhinoceros. The most rhinocerosy of them can be 80mm long and weigh 35 grams and Mrs Noah must have struggled to resist the urge to kill them with her broom.

Now Dr David Rentz, AM, the distinguished entomologist (he's a broadcaster too, and an Ig-Nobel Laureate), has written A Guide to the Cockroaches of Australia. At its launch at the CSIRO and as the author spoke (sitting next to a display case of deceased monster cockroaches) one was reminded of how while some people are often younger than they look Rentz is far younger than he sounds. An American (although living in Australia for ages, including decades in Canberra when he was, among other things, a curator of orthopteroid insects for the Australian National Insect Collection) he has a lovely, velvety, foggy voice that makes him sound the way 250-year-old Old Testament prophets might have sounded (if they'd grown up in the US). It is worth listening to his down-memory-lane weekly radio show, The Hit Parade of Yesterday, just to hear his voice.

Rentz knows that he will struggle to get most of us to share his enthusiasm for cockroaches.

"When I told a friend that I was writing a book on cockroaches he looked at me in horror, and he

Why are cockroaches so maligned?

"It's that people are only familiar with the six species that cause problems. They give the whole group a bad name, like a few nasty bikies giving a bad name to everyone who rides a motorcycle, or like the few rotten politicians that poison our minds against all of them. But when you see how beautifully coloured some of them are when they're photographed up close [and the book is a gallery of these pin-ups] you will change your opinion about the group. I hope!

"Actually, in Canberra [there about 20 species endemic to the ACT] there are just one or two species that enter human habitations. The ones that may be attracted to your lights on a summer evening, they'll be dead by the morning because there's nothing for them to eat and they don't like dry conditions. So a lot of the cockroaches that people see are not worth worrying about really. But when there are cockroaches in hospitals and restaurants, in hotels and kitchens, then they should be dealt with. They can spread diseases especially if they've been walking about in disease-carrying stuff and then get on to food.

"You don't want cockroach infestations in your kitchen, but out in nature they are very important because there are so many of them. If you were to go up on Black Mountain and pick up a handful of leaf litter chances are there will be some small cockroaches in that handful. They're the recyclers. They're converting leaves into soil."

Although the three years of compiling the book have been enormous fun ("I've enjoyed every minute of it") he has, too, been on a kind of a mission. Time is running out. There are so many cockroaches and so few people studying them. The big impetus for the book has been the sad fact that taxonomists (the scientists who carefully identify and name species) are what he calls "a dying breed".

"Around the world and especially in Australia taxonomic positions are evaporating, and there are only two other people in Australia studying cockroaches. So I thought I should get all that's known about them [his book acknowledges great cockroach scholars who have gone before] all together in one book and hope that the book will establish interest in them for other generations."

But in spite of the melancholy urgency involved it has been lots of fun. So, for example, when he found there were not enough known photographs of cockroach species for his book he not only sent out a general SOS to all the amateur and professional field naturalist paparazzi (this columnist's word) who might have photographs, but with a colleague began doing many, many field trips in the cockroach-rich hinterland of Cairns, "on hands and knees, looking for cockroaches to photograph".

The urgent need for photographs was, he laughs, "the carrot leading the jackass" on these blissful expeditions.

Dave Rentz's A Guide To The Cockroaches Of Australia is published by the CSIRO and will go on sale any day now in discerning bookshops.