Available evidence on worm lizard (Amphisbaenia) density from systematic surveys and opportunistic records

The subterranean lifestyle of amphisbaenians limits ecological sampling, leading to sparse, methodologically heterogeneous estimates of population density. We reviewed available literature reporting on amphisbaenian density. Only a limited number of studies provide density estimates based on clearly defined sampled areas, mostly from southern Africa and typically expressed at the scale of square meters. Reported values reflect differences in methodology, excavation depth, habitat suitability, and spatial scale rather than true biological variation. Additional evidence from non-systematic excavation and surface sampling suggests that amphisbaenians may reach high local abundance where suitable subterranean habitat is available, although such data cannot be reliably converted into density estimates. Estimates derived from agricultural plowing or bulldozing, as part of environmental licensing, although usually based on several specimens, often yield lower apparent densities, likely due to incomplete detection and the inclusion of unsuitable habitat. Improved reporting standards and the careful publication of opportunistic data could substantially advance knowledge of amphisbaenian natural history.