Why Mosquitoes and Mild Winters Don't Mix

Learn how to handle an early mosquito hatch.

By Emily Main


Wild winters make for more mosquitoesWhen it comes to mosquito diseases, West Nile virus tends to get all the headline-grabbing attention. It's probably the most common disease spread by the little bloodsuckers, at least here in the U.S. Incidences of West Nile peak in August in September, when mosquitoes transition from sucking the blood of birds (their meal of choice for the early part of the summer) to sucking the blood of people and other mammals.

But according to a new study published in the journal Biology Letters, the mild winter we've just had may speed up that transition, and that could lead to a higher incidence of mosquito-borne diseases this year.

The authors trapped one particular mosquito species, C. erraticus for eight years, testing the DNA of the blood in the mosquitoes they trapped so it could be traced back to the source. In warmer years, the mosquitoes transitioned from biting birds to biting mammals in May or June, whereas in cooler years, the transition happened in August and September.

With a warm spring arriving on the heels of a mild winter this year, mosquito populations are likely to sprout earlier and thus transition to a human-based diet earlier than they normally do. And it's not just West Nile virus that they could bring with them. The species of mosquito studied here carries the uncommon but fatal disease eastern equine encephalitis. Carried by birds, the disease spreads to humans after they are bitten by a mosquito that has also bitten an infected horse. Although just a few cases are reported in the U.S. each year, 33 percent of infected people die from it, and it can leave survivors with significant brain damage.

Photo: (cc) dr_relling/Flickr