The sandy beaches of Ärjänsaari Island are shaped by the ice, waves, the wind and the blazing sun, creating special, changing conditions that are demanding for species. However, the sand dunes, the herb-rich forests where the baneberry (*Actaea*) thrives and the light-filled pine forests provide favourable habitats for many invertebrates.

Ärjänsaari Island is home to insect species that require sheltered, sun-exposed environments and dunes. In addition, the vegetation must remain partly covered by sand. This is why the island’s shores are managed, not allowing them to become overgrown.
The sand dunes in the Säippä and Kirkkosäikkä tips of peninsulas offer potential sun-exposed habitats for insects, but the species have not yet been thoroughly studied. In a study of insects that was carried out in the summer of 2018, a total of 314 insect species were sighted on the island. Out of them, the share of butterflies and moths was 204 species. In addition, there were 29 species of *Hymenopetra*, 49 beetle species, 4 species of *Diptera*, 10 species of *Heteroptera* and 18 species of *Auchenorrhyncha*.
Six threatened and near-threatened butterfly and moth species were sighted. Three of them were spotted in the Kainuu region for the first time. One of them is an endangered moth species *Schytris empetrella*, which lives on dunes covered by crowberries (*Empetrum nigrum*).
The population of *Scythris empetrella* on Ärjänsaari Island is the only known population in inland Finland. Besides the island, it is only sighted in a few places on seaside dunes of the Bothnian Bay and the Gulf of Finland.
The following species that were new to the Kainuu region were also sighted: *Etainia albibimaculella* and *Coleophora arctostaphyli*.
The most common moths were great grey dart (*Eurois occulta*), the rosy rustic (*Hydraecia micacea*) and the knot grass moth (*Acronicta rumicis*).
The study of insects was continued on Ärjänsaari Island in the summer of 2019. The study was part of the project "Paratiisin ovet aukeavat" that was implemented by Metsähallitus. The project was funded by the Oulujärvi LEADER association from the European Agricultural Fund for Rural Development (EAFRD).

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