Hydrachnidia water mites were examined in eight streams with similar chemistry from two sub-catchments that did not differ with respect to precipitation predictability (P>0.05). This study describes the structure of this taxonomic segment of the invertebrate community as species diversity, relative abundance, and composition. Twenty-two water mite species were found in this study. Following rarefaction to sub-samples of 170 individuals, expected richness for these eight subtropical streams was lower (E<16) than found for a tropical stream (E=23). Species composition and the log-normal distribution of species were similar in the two subcatchments. However, richness and diversity show significant differences between the two sub-catchments (P<0.05). The results suggest that similar seasonal rainfall pattern (contingency>65%) does not guarantee similar patterns of diversity and richness in neighboring sub-catchments.