Believe it or not, the mosquitoes are out there, even in winter. They're just hiding so we don't notice them. Absent unseasonably warm weather, mosquitoes remain inactive through the winter months.
Some mosquitoes lay winter hardy eggs which lie dormant in the soil until spring. In late summer or fall, the female mosquito lays her eggs singly in areas where the ground is moist. The eggs hatch when conditions become favorable again, usually in the spring when temperatures begin to rise and sufficient rain falls.
Certain mosquitoes can survive winter in the larval stage. All mosquito larvae require water, even in winter. As the water temperature drops, it induces a state of diapause in the mosquito larvae, suspending further development and slowing metabolism. Development resumes when the water warms again.