What happens to mosquitoes in the winter?

Concerns over Zika virus in the U.S. were at the forefront of public health conversations this year. But what happens when the temperature drops? Do mosquitoes and the diseases they carry such as Zika virus just simply go away? Well, not exactly, says the National Pest Management Association (NPMA).

According to the NPMA, how mosquitoes survive the winter differs by species. “Some mosquitoes may overwinter as adults, hibernating in places like hollow logs or burrows created by other animals. Other species may endure the winter in immature life stages, such as larvae and pupa, remaining in a state of diapause, suspending their development during the coldest months,” said Dr. Michael Bentley, staff entomologist for the NPMA.

Carriers of Zika, including the yellow fever and Asian tiger mosquitoes, overwinter in the egg stage, which means as days get shorter and temperatures begin to fall, the last surviving adult females lay their eggs in water-holding containers. The adults eventually die off while the next generation overwinters in the egg stage, waiting to hatch the following spring.

“The newly-deposited eggs survive the winter because they can withstand several months without water, as well as relatively cold conditions,” said Bentley. “As temperatures start to rise and rainfall picks back up again in spring, the eggs are re-submerged and hatch to start the next generation.”

This survival can create implications when the eggs come from an infected mosquito. In fact, a study published in the American Journal of Tropical Medicine and Hygiene found evidence that an infected female mosquito could pass Zika onto her offspring.

“Because the Zika-carrying, Aedes species of mosquitoes overwinter in the egg stage, it could be possible for infected females to lay some eggs that could survive the winter and emerge as diseased adults the following spring,” said Bentley.

The NPMA recommends that homeowners take preventative measures, even in the fall and winter, by inspecting properties for any containers they can remove and keep from holding water. These water collection sites can be harboring eggs. “Mosquitoes need only half an inch of standing water or enough water to fill a soda cap,” said Bentley.

Although mosquitoes may be out of sight, they are waiting it out for spring.