It may come as something of a surprise but the area inland from Royan can suffer badly some years from mosquitoes - the large areas of standing water in the Marais provide a breeding ground for these insects. Mosquities can be seen in the area from early Spring depending on weather conditions.
A website has been set up which gives up to date information (in French) about the levels of mosquitoes in each region. This link is the page for Charente-Maritime which includes Royan. The French for mosquito is les moustiques.
It is probably a good idea to go prepared if you are sensitive to mosquito bites particularly if you are staying in the countryside inland from Royan.