I have spent less time in the arid zone in the last few years than I did during the 1960's, 1970's and early 1980's. This results from a progression through age and a career structure which gradually shifted the emphasis of my work from being essentially field-oriented to essentially office-hound. When, therefore, I was asked by John Cloudsley-Thompson to undertake the writing of this hook I hesitated for two reasons. One reason was that, although I now had access to good library facilities and kept up with the literature on the arid zones and their fauna, I was not sure that a sedentary and...