In late August 2010, an increase in mosquito activity was reported in the Nantes metropolitan area. The species in question was likely Aedes caspius. Similar incidents had been reported previously and attributed to mosquitoes migrating from the Loire estuary. Since this episode had a significant impact on the operations of SOS Médecins Nantes, the Cire conducted a retrospective study covering the past 16 years based on SOS Médecins Nantes’s data, in collaboration with EID Atlantique and Météo France, in order to: 1) determine the frequency and characteristics of mosquito bite outbreaks in Nantes; 2) to identify the meteorological factors that first promote egg hatching along the Loire estuary, and subsequently mosquito bite outbreaks in Nantes. Over the 16-year study period, seven periods of mosquito bite outbreaks were identified, lasting between 2 and 4 days. Only the presence of a high tide was significantly associated with mosquito egg hatching. Two factors favored biting epidemics in the Nantes metropolitan area: very high tides (threshold at 108) and westerly winds on the days following a hatch. This study demonstrated a low frequency of these outbreaks and identified a predictive threshold for the tidal coefficient regarding the risk of Ae. caspius bite outbreaks in the Nantes metropolitan area during the summer months. Although Ae. caspius are currently known primarily for being a nuisance, this study provides insights into the factors facilitating their movement from the Loire estuary to Nantes, which may be useful in the event of a risk of vector-borne disease transmission by these mosquitoes, which have the potential to do so. (R.A.)