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Island biogeography is based on the idea that the larger an island, and the less it is isolated from other areas, the higher the biodiversity it contains. The premise of island size contributing to diversity is based on the fundamental ecological concept—the species area relationship (SAR). Wetlands and, in particular, arid zone spring wetlands can be considered islands as they are wetted habitat surrounded by a harsh and dry landscape—“girt by dirt”—forming an ideal setting to study island biogeography. While studies in spring wetlands have identified SARs that conform to the concept, others identified conflicting information. The aim of our study was to assess the relationship between spring wetland wetted area and its aquatic invertebrate taxonomic richness across three of Australia’s Great Artesian Basin spring complexes. Wetted area and aquatic invertebrates were recorded for 32 individual spring wetlands. The constraint that wetted area has on invertebrate taxonomic richness was analysed using quantile regression. ANOSIM was used to compare differences in the invertebrate community between spring complexes. No significant relationship between wetted area and taxonomic richness was identified across all springs, but the aquatic invertebrate community and taxonomic richness was significantly different across the three spring complexes. Analyses were repeated for one spring complex. Increasing wetland size was found to constrain invertebrate taxonomic richness at Edgbaston Springs. These results contrast with the basic SAR concept but can potentially be the result of a “small island effect” where the relationship is overridden by anthropogenic disturbance.