What do mosquitoes DO all winter?

If you have been following the Eastern equine encephalitis outbreak in the Northeast US, most of the news stories end with a statement such as “the first killing frost ends the adult mosquito season in any given area.” This is a completely valid assumption when you live in an area where temperatures drop below freezing and stay there for weeks at a time.

However, to say that winter weather in our region can be variable is an understatement. While our recent cold front may have frozen some tender plants, it wasn’t enough to do much damage to our resident population of southern house mosquitoes, Culex quinquefasciatus.

A technician collects mosquitoes resting underneath a bridge

That’s because, as the days get shorter and temperatures and humidity drop, this last generation of female mosquitoes plump up internal fat reserves and find a nice sheltered spot to wait out the winter. Storm drains are a favorite haunt, along with garden sheds and rodent burrows.

The southern house mosquito, Culex quinquefasciatus, overwinters as an adult fed by fat reserves in her abdomen

Along with a thicker outer skeleton that resists drying and a metabolism slowed down like cold molasses, these mosquitoes enter a form of dormancy called diapause. This state of suspended development will last until the days lengthen and temperatures rise again – a relatively short window in SE Texas.

And that sheltered spot? When it warms up, storm drains do double duty as a breeding place for those overwintering mosquitoes. Excess irrigation and grass clippings keep drains perpetually moist and full of organic material. This creates the perfect breeding ground– read more about it here. Consider turning off your automatic sprinkler for the winter to avoid runoff (it’s also healthier for your lawn).

Mosquitoes shelter in storm drains over the winter, which become breeding grounds in the spring if kept wet by irrigation run-off

So how do mosquitoes survive where it is cold and below freezing? They do so as eggs, just like the invasive Asian tiger mosquito, Aedes albopictus, that we have here. Based on seasonal cues, females will lay eggs with more fat to sustain the embryo, along with a thicker “coat” to keep eggs from drying out so they can survive the colder temperatures. These eggs are as big as a speck of dirt and almost impossible to differentiate with the naked eye. So, do yourself a favor and give those plant pots and other outdoor items a good scrub before storing them away for the winter. You’ll be rewarded with fewer mosquitoes when the weather warms.   


Questions? Comments? Contact enviro@thewoodlandstownship-tx.gov

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