Ground truthing in Madagascar and Namibia shows remote sensing alone cannot reliably identify fairy circles

Fairy circles are defined as barren gaps in grasslands that lack central insect-nest structures, characterized by highly ordered, spatially periodic patterns. These unique vegetation gaps occur exclusively in the Namib Desert and in a small region of Western Australia. Identifying new occurrences of fairy circles requires ground-truthing to verify the presence of genuine examples. In this study, we present two African cases that highlight the need for ground-truthing. Recently, Guirado et al. (2023) reported 263 additional vegetation-gap sites globally, labeling them as “fairy circle-like” patterns. However, their study relied only on remote sensing rather than field observations and did not address the mechanisms behind these patterns. They excluded sites with visible termite mounds from their classification. In our investigation of one such site in Madagascar, we found that most gaps contain mounds of the grass-feeding termite Coarctotermes clepsydra, while their bare surfaces are covered by thick biocrust. Unlike the highly ordered fairy circles of Namibia and Australia, the Malagasy grassland gaps are irregularly spaced and contain termite mounds, disqualifying them as fairy circles. Biocrust development enhances runoff from the gap centers, supplying additional water to the grass and likely increasing resilience during droughts. In another study, Meyer et al. (2025) presented satellite images of Euphorbia shrubs and barren patches in Namibia, mistakenly identified as “new fairy circles.” Our field visit showed that these vegetation gaps contained significant Euphorbia branches and vigorous grass growth, contradicting the definition of fairy circles. All patches exhibited a strongly convex shape, containing piles of elevated sand, contrary to the definition of fairy circles. Our findings emphasize that Namibian and Australian fairy circles represent a distinct class of vegetation-gap patterns, separate from termite-driven gaps in Madagascar or Euphorbia-related vegetation gaps in Namibia. Broader field-based studies are essential for accurately classifying new fairy circles in global surveys.