Habitat loss and degradation are among the key drivers of biodiversity loss worldwide. As an example, many butterfly species that depend on specific host plants to lay their eggs upon, or that only occur at particular habitats, have sharply declined across Europe. In such context, organisms capable of shaping the environment with their activity – so-called ecosystem engineers – may represent valuable allies to biodiversity conservation as they can create suitable microhabitat to endangered butterflies.

One of the most spread ecosystem engineers in Europe is the wild boar, whose rooting activity may significantly change soil conditions and, in turn, vegetation and microhabitats. Wild boars are increasingly raising concerns among conservationists due to their potentially negative effects on the environment, especially on vegetation, yet very little is known on how rooting affects other animals, such as insects of conservation concern.

In this work, we used the endemic Italian festoon (Zerynthia cassandra) as a case-study to investigate how wild boars may favor – or not – a protected butterfly species with narrow environmental needs. The Italian festoon is in fact a specialized butterfly that only lays eggs on a few herbaceous species from the genus Aristolochia, and due to its low abundance is listed among the species protected by the EU Habitats Directive.

To tackle this, we conducted our work in grassland habitats of southern Italy, where we intensively surveyed sites affected or not affected by wild boar rooting activity for recording the abundance of the host plant (Aristolochia clusii), the occurrence of the butterfly eggs, and the herbaceous plant community.

We highlighted that the host plant is more likely to occur at sites with wild boar activity, where it is also more abundant. The Italian festoon also prefers to lay eggs on host plants surrounded by larger extents of rooting, which also combines with an increased availability of suitable nectar resources.

Our results point at the wild boar as a key ally to the Italian festoon, at least in the study area, and represent a first step in understanding the subtle and delicate connections among ecosystem engineers, plants and invertebrates. Potential further research avenues on this system may focus on identifying the optimum level of wild boar rooting activity – and population density – that fosters positive responses by species and habitats of conservation concern, i.e. providing a tool for a more informed boar management.