Special features resembling internal hollows (niches-like ephemeral gully head) are common in the collapsing walls of granite Benggang erosion in southern China. This study investigated the material conditions and drivers of niches occurrence by describing the morphological evolution of the niches, and combined with moment analysis methods to construct mechanical models to evaluate the stability of collapsing walls and niches. Studies have shown that niches morphology evolves through three stages of "embryonic-development-formation". Soil heterogeneity in the profile is the underlying condition for niche development, with hydrodynamics and gravity acting together as external factors to drive niche development. The stability of the niche decreases as its height increases and its angle decreases. The development of niches may be a sign of the initiation of headcut erosion of the Benggang, and the containment of niche formation is conducive to improving the stability of the collapsing wall. The results of the study provide a theoretical basis for Benggang erosion management.