Wasp and Hornet Nests as Biomonitoring Tools: Elemental Composition and Temporal Trends

The rapid expansion of industrial and agricultural activities, combined with urbanization and traffic emissions, is leading to increased pollution [1]. Toxic metals are of particular concern, as they persist in ecosystems and pose risks to biodiversity and human health [2]. While social insects are increasingly used as bioindicators, their nests remain unexplored as biomonitoring matrices despite clear advantages as nests can be collected non-destructively after colony decline. Hornet (Vespa crabro) nests, which are built layer by layer during the active season, are of particular interest as they may capture temporal variations in contamination. In this study, we compared the elemental composition of German wasp (Vespula germanica) and hornet nests collected at the same site, to determine which nests accumulate more potentially toxic metals and whether hornet nests can serve as seasonal recorders of environmental change. Element concentrations were determined using inductively coupled plasma mass spectrometry (ICP-MS). Wasp nests were analyzed as whole samples, while hornet nests were broken down into their structural components: base (B), outer envelope (OE), and successive comb layers (L1–L10). Our results showed clear differences between species. Wasp nests contained significantly higher concentrations of most major and trace elements, including Li, Mg, Al, P, S, K, Ca, V, Fe, Co, Ni, Zn, As, Se, Rb, Mo, Ag, Cd, and Cs, suggesting a strong accumulation capacity. In contrast, hornet nests had lower overall concentrations but clear stratification between layers. For example, Na concentrations were higher in the late comb layers (L9) than in the early ones (L2–L4), Mn and Cu were more enriched in L1–L4 than in the outer envelope, Cd was elevated in L2 compared to the envelope, and Tl showed peaks in L5–L6. Boron was the only element that was consistently more abundant in hornet nests than in wasp nests, with particularly high values in L8. These inter- and intraspecific differences are likely due to differences in nest construction materials [3-5], prey selection, and the accumulation of larval remains such as exuviae and feces. Both V. crabro and V. germanica collect carbohydrate-rich resources (nectar, honeydew, sap, ripe fruit) and protein- and lipid-rich prey (arthropods), but their dietary preferences and feeding behavior differ, which in turn affects nest composition. Taken together, our results show that while wasp nests have a higher absolute load of metals, hornet nests provide a unique temporal resolution, by recording seasonal variations in environmental contamination. This dual value, high accumulation in wasp nests and temporal stratification in hornet nests, suggests that social insect nests provide an ethical, practical, and highly informative resource for biomonitoring toxic elements in terrestrial ecosystems.