10 October 2017

From 17 to 27 September, PonDerat staff carried out the second monitoring of terrestrial invertebrates on the islands of Ponza, Palmarola, Ventotene and Santo Stefano. The objectives, once again, were gasteropods and terrestrial arthropods potentially impacted by rat predation.

The investigation focused on the same sites sampled during the spring session and followed the same methods: entomological net and pitfall traps for terrestrial arthropods, direct collection on pre-defined plots for terrestrial gastropods.

Arthropod sampling was more successful than spring sampling in terms of abundance of species and observed individuals. Many orthopterans, mantises and spiders have been collected and observed, leading to a challenging work of identification in the lab.

As for gasteropods, results confirm what emerged in the spring survey. Ventotene and Santo Stefano seem much richer of molluscs, both in terms of number of species and abundance of individuals, compared to Ponza and Palmarola, probably due to their different geological nature. The higher humidity led to the collection of more specimens, especially snails. The most interesting thing, according to technicians, was the observation of some rats and the discovery of some rat burrows with several shells of predated snails in Ponza, Palmarola and Ventotene. The observation of a larger number of gnawed snail shells compared to spring survey suggests a more intense predation of rats on snails in the summer, when the availability of typical food sources, such as dead or debilitated migratory birds, shoots and seeds, is reduced.

The following laboratory phase aimed at analyzing and identifying collected samples will allow to complete the knowledge framework before the start of eradication activities.