Scientific note: Direct evidence of cryptic refugia for post-fire population recovery in snail-shell-nesting bees

This is the authors' abstract. We don't add key points for this paper.

Wildfires are increasingly recognized as a key threat to bee populations, especially in the fire-prone Mediterranean shrublands. Post‑fire recovery of plant–pollinator networks depends on both floral resource dynamics and the availability of fire refugia, yet the latter remains poorly documented for cavity‑nesting bees. Here we report an unforeseen case study showing that screes act as effective cryptic refugia for snail‑shell‑nesting bees in a protected shrubland. While monitoring nests of the obligate snail‑shell‑nesting bee Rhodanthidium sticticum in summer 2025, a 72‑ha wildfire burnt one of our experimental sites. In this context, we could examine and compare the fate of 123 nests in a complete Before-After Control-Impact (BACI) design. We found direct evidence that nests can survive fire in specific microhabitats, and further provide estimates of their survival probability. All nests in exposed litter were destroyed, whereas most nests located under stone shelters remained structurally intact. Subsequent dissection revealed that 35% (19–54%) of nests in such protective microhabitats may survive and successfully produce adults after fire. This survival rate is significantly less than in unburnt controls (range 67–87%) but far exceeds the total mortality for unprotected nests. Published studies on gastropods and complementary field surveys support the interpretation that stones and boulders in screes provide effective and predictable fire refugia for snails as well. We argue that Mediterranean screes deserve explicit recognition and protection in post‑fire management and monitoring as key habitats for the persistence and recovery of these specialized bee–snail associations.