Hu et al. (1) propose that vegetation growth in "kernel” regions of the Savanna/Sahel during January/February is key to explain population abundances of the painted lady butterfly (Vanessa cardui) in Europe. We identify issues in their rationale and provide evidence toward an alternative scenario. First, Hu et al. (1) conjecture that, in exceptional years, substantial breeding of V. cardui occurs in the African Savanna/Sahel at the peak of the dry season, but no ground-truthed evidence is provided. This hypothesis challenges previous research in Africa, including models based on breeding data (2, 3), and the authors refer to their results as "counterintuitive.” We inspected the leaf area index (LAI) in Hu et al.'s kernels and show that the values are steadily low, with no peaks in the dry season that may indicate substantial herbaceous coverage at any scale (Fig. 1A). We argue that the low signal of vegetation growth found by Hu et al. likely corresponds to woody plants (Fig. 1B), which may store water (4, 5) but are not V. cardui larval hosts (2, 3).
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