Mosquitos thrive on moisture, so they are worse during the rainy season, which is normally June through October. We seem to have more rain in the winter months than we used to, so they can appear at any time of the year, but they also don't like the cold, so even when it rains in the winter there are fewer. Be sure to travel with mosquito repellant no matter when you come, keep it with you all the time, and you will be fine. They are also worse at dawn and dusk and they are attracted to dark clothing.
Yucatan Today Editor