Seems quite random. The first few years that i had holidays in Crete ( spring, summer, autumn) there were NO mosquitos and i thought it was amazing and that maybe we were lucky in the area we stayed in. In the last few years , since deciding to buy here, i have seen loads of them and last year i got so badly bitten ( in August) i still have scars on my arms and legs. Since then i have been ultra careful, but i noticed loads of them in May. And wasps too! Here in the UK we have had a bumper year for wasps, and hornets, due to the long intense heatwave or so they say. I really hate them all!!!